Dataset for Pathology Reporting of Colorectal Cancer

Objective: The aim of this study to describe a new international dataset for pathology reporting of colorectal cancer surgical specimens, produced under the auspices of the International Collaboration on Cancer Reporting (ICCR).Background: Quality of pathology reporting and mutual understanding between colorectal surgeon, pathologist and oncologist are vital to patient management. Some pathology parameters are prone to variable interpretation, resulting in differing positions adopted by existing national datasets. Methods: The ICCR, a global alliance of major pathology institutions with links to international cancer organizations, has developed and ratified a rigorous and efficient process for the development of evidence-based, structured datasets for pathology reporting of common cancers. Here we describe the production of a dataset for colorectal cancer resection specimens by a multidisciplinary panel of internationally recognized experts. Results: The agreed dataset comprises eighteen core (essential) and seven non-core (recommended) elements identified from a review of current evidence. Areas of contention are addressed, some highly relevant to surgical practice, with the aim of standardizing multidisciplinary discussion. The summation of all core elements is considered to be the minimum reporting standard for individual cases. Commentary is provided, explaining each element's clinical relevance, definitions to be applied where appropriate for the agreed list of value options and the rationale for considering the element as core or non-core. Conclusions: This first internationally agreed dataset for colorectal cancer pathology reporting promotes standardization of pathology reporting and enhanced clinicopathological communication. Widespread adoption will facilitate international comparisons, multinational clinical trials and help to improve the management of colorectal cancer globally.(Ann Surg 2022;275:e549-e561) P athology reporting of cancer resection specimens, through provision of histological subtype, grade, stage, and other clinically relevant information, impacts on individual patient management and prognosis. At a population level, it provides data for cancer registrations, epidemiological audits, and research including clinical trials. 1,2 Tissue-based cancer research also partly relies on histopathological stage, the presence high-risk features, and molecular pathological subtypes. Standardization of pathology evaluation of cancer resection specimens and reporting of individual features is essential, to allow valid comparison of data between cohorts and countries, to allow assessment of the impact of new screening programs and to allow participation in multicenter trials. However, some pathology parameters are prone to variable or evolving interpretation, resulting in differing positions adopted by various national From the
datasets in existence or an inability to reach consensus, manifest as a lack of clearly expressed guidance for certain contentious areas. This is evidenced by regular changes made to TNM staging systems as new evidence and new interpretations emerge. For some issues, clear guidance is simply unavailable.
All of these principles apply to colorectal cancer (CRC) and some such issues impact directly on surgical practice and staging. For example, the minimum distance of tumor from a margin required to label as ''clear,'' the interpretation of regional, discontinuous ''tumor deposits,'' and the interpretation of surgical resection margin status when this is involved by tumor not continuous with the primary tumor. [bib_ref] The future of the TNM staging system in colorectal cancer: time for..., Quirke [/bib_ref] If there is limited evidence, clear consensus-based guidelines, based on best available evidence and expert opinion, are helpful to assist pathologists in case by case reporting and surgeons and oncologists in clinical management of their patients. Close liaison between surgeon and pathologist, and good surgical understanding of pathology reporting guidelines and practice are key to maximizing the quality of pathology reports and their value to the surgeon and ultimately the patient.
Pathology protocols and datasets are well established in some countries and have been independently developed at national level by organizations including the College of American Pathologists (CAP), USA, the Royal College of Pathologists (RCPath), United Kingdom (UK), and the Royal College of Pathologists of Australasia (RCPA). Although these organizations' protocols broadly align, there are significant differences in structure, content and terminology and some subtle differences in interpretation that could hinder international comparison. Standardization of existing national cancer reporting datasets would also have the added benefits of reducing the global burden of regular dataset production and of providing a single benchmarking reference available to other countries.
With this in mind, in 2011, a number of pathology organizations including the CAP, RCPath, and RCPA formed the International Collaboration on Cancer Reporting (ICCR) and successfully piloted the development of datasets for pathology reporting of a select number of cancers. The subsequent ICCR development has been described previously in detail. [bib_ref] Pathology data set for reporting parathyroid carcinoma and atypical parathyroid neoplasm: recommendations..., Williams [/bib_ref] The ICCR has developed important strategic alliances with other international cancer organizations including the International Agency for Research on Cancer (IARC) which is responsible for producing the World Health Organization (WHO) monographs or ''Blue Books'' on tumor classification and the Union for International Cancer Control (UICC) and American Joint Committee on Cancer (AJCC). These partnerships facilitate the co-ordination of dataset production with new classifications and staging systems. The ICCR datasets are freely available from the ICCR website (http:// www.iccr-cancer.org/datasets). Here we describe the production of such a dataset for CRC surgical resection specimens by a panel of internationally recognized expert pathologists and other clinicians, supported by the ICCR. Areas of contention or divergence are addressed, with the aim of offering a consensus position to standardize interpretation and multidisciplinary discussion.

# Methods
The ICCR has developed a rigorous process for the production of individual datasets (http://www.iccr-cancer.org/datasets/dataset-development). This process has been described in detail in previous publications (http://www.iccr-cancer.org/articles/publications). The ICCR quality framework dictates both content and presentation and the roles and responsibilities of all involved are clearly outlined. In brief, the Dataset Steering Committee (DSC) of the ICCR appointed a ''Series Lead authors of the current CAP, RCPath, and RCPA CRC datasets were included.The group was coordinated by an ICCR Project Manager (F.W.), assuring optimal communication within the international group and adherence to agreed timelines.
Regarding scope, this dataset was developed for the reporting of pathology specimens resulting from major surgical resection of primary carcinomas arising within the colon and rectum. This includes neuroendocrine carcinomas (NECs) and mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs). [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] It is not applicable to carcinomas of the small intestine, appendix or anus, nor to neuroendocrine tumors (NETs) or nonepithelial malignancies, as these are subject to different classifications and staging systems. Furthermore, primary CRC treated by local excision are the subject of a separate ICCR dataset, as specimen handling and reporting of these differ from major surgical resection specimens.
An initial draft document was produced by the Project Manager and Chair after scrutiny of core and non-core data items within existing CAP, RCPath, and RCPA CRC datasets and review of present published evidence. This draft was circulated and individual dataset items discussed among the DAC at a coordinated series of teleconferences, following which an agreed draft dataset was posted for open international consultation on the ICCR website for a period of 2 months. All comments received were discussed by the DAC and, where agreed, resultant changes incorporated into the final dataset, which was ratified by the DSC before publication. The final agreed dataset is available at http://www.iccr-cancer.org/datasets/publisheddatasets/digestive-tract/colorectal.
The ICCR dataset style lists a set of reporting elements and value lists (responses) accompanied by a commentary for each, explaining the element and categorization, offering guidance for reporting, citing relevant evidence, and, where applicable, definitions for the value lists. Each element is categorized as either core or noncore. Core elements are those unanimously agreed by the expert panel to be essential for diagnosis, prognostication and/or patient management. These generally required evidentiary support at Level III-2 or above [based on prognostic factors in the National Health and Medical Research Council (NHMRC) levels of evidence document, and defined as ''Analysis of prognostic factors amongst persons in a single arm of a randomized controlled trial'']. [bib_ref] Extending an evidence hierarchy to include topics other than treatment: revising the..., Merlin [/bib_ref] Non-core elements were those that did not meet the above criterion but were considered by the panel to be clinically important, representing good practice but not currently fully validated for routine clinical practice. Specific levels of evidence were not assigned to each core or non-core element. The summation of all core elements is considered to be the minimum reporting standard for individual cases.

# Results
A summary of the agreed core and non-core elements is presented in [fig_ref] TABLE 1: Core and Non-Core Elements for ReportingThese items are only relevant to certain... [/fig_ref] and each is described in further detail below:

## Clinical information
Knowledge of relevant clinical information, such as an underlying polyposis syndrome, Lynch syndrome or chronic inflammatory bowel disease, is essential for optimal specimen sampling and histological interpretation. However, as it is beyond the control of the pathologist to ensure this information is available, it is considered a non-core rather than a core item.
Two specific items represent exceptions to this rule, given their importance, and are considered core. Firstly, information on neoadjuvant therapy, including type and duration, is a core item and must always be provided to the pathologist, as response to therapy can influence stage and tumor morphology, potentially altering interpretation. Staging should be provided with a ''y'' prefix.
Secondly, the nature of the operative procedure is a core item [fig_ref] TABLE 1: Core and Non-Core Elements for ReportingThese items are only relevant to certain... [/fig_ref] , and additional information may be provided clinically, such as the attempted dissection plane in an abdominoperineal excision. Distinction of high from low anterior resection, the latter defined by inclusion of the peritoneal reflection within the specimen, is considered non-core. If the operative specimen includes any additional tissue or organs, for example en bloc resection of a separate segment of intestine or abdominal wall connective tissue or a more extensive anterior exenteration specimen [fig_ref] FIGURE 1: A fresh anterior exenteration specimen comprising abdominoperineal excision of the rectum and... [/fig_ref] , details of all organs present within the submitted specimen should be clearly stated on the specimen request form.

## Tumor site
If a specimen contains multiple tumors, these should all be documented individually and separate datasets completed for each. Tumor location is a core item, stated in the clinical information provided and confirmed by macroscopic specimen examination. It can be difficult to identify specific location in the colon within an ex vivo specimen, particularly in relation to the flexures. If clinical and pathological tumor locations are discordant, this should be documented by photography and discussed with the clinical team. Recording the anatomical site allows correlation with prior endoscopic and radiological investigations, indicates whether or not a nonperitonealized margin is likely to be present and permits classification of lymph nodes as regional versus nonregional. Distinction of colonic from rectal origin is of importance, given different biology, clinical features, management, and risks of peritoneal versus local recurrence. This classification can be subjective, especially for more advanced stage tumors. If a tumor straddles 2 sites, the site with the greatest tumor bulk should be recorded. The rectosigmoid boundary is marked by fusion of the three taeniae coli of the sigmoid colon to form the circumferential longitudinal muscle of the rectal wall. If advanced tumor growth obliterates these anatomical landmarks, the tumor site should be retrieved from available clinical and radiological information. [bib_ref] Definition of the rectum: an international, expert-based Delphi consensus, D&apos;souza [/bib_ref] Classification as rectosigmoid should be reserved for cases in which an accurate determination between rectum and sigmoid cannot be made by above methods.

## Tumor dimensions
Tumor size has no prognostic significance for CRC and does not directly influence staging. Despite this, maximum dimension is considered a core data item, as it is baseline information which allows correlation with preoperative clinical, endoscopic, and radiological assessments. It should be based on a combination of macroscopic and microscopic assessment and, if possible, exclude any associated inflammatory component or preinvasive lesion, which may be noted in a comment for clinicopathological correlation. Additional tumor dimensions may be provided as non-core data.

## Perforation
Tumor perforation into the peritoneal cavity is a well-established adverse prognostic factor in CRC [bib_ref] Identification of objective pathological prognostic determinants and models of prognosis in Dukes'..., Petersen [/bib_ref] [bib_ref] Low rectal cancer: a call for a change of approach in abdominoperineal..., Nagtegaal [/bib_ref] and its presence or absence should be recorded as a core item. Tumor perforation is defined as a macroscopically visible full thickness defect, such that the bowel lumen within the segment involved by tumor is in communication with the external surface of the resection specimen or with the lumen of another organ. Cases with tumor perforation are regarded as pT4a.Note that tumor perforation requires penetration of the serosal surface. Peritumoral abscess cavity, for example, within the mesentery, that is contained and does not demonstrate breach of the serosal surface, is not considered perforation and is considered pT3 rather than pT4a. This may be commonly encountered in the setting of sigmoid diverticular disease complicated by CRC. Perforation of the colon resulting from a more distal obstructing tumor is distinct from tumor perforation and is not interpreted as pT4 disease. However, this should still be recorded as nontumor perforation is associated with higher mortality risk.
Some confusion can be introduced when using the term perforation for other settings, such as when a full thickness defect arises intraoperatively. We consider the term perforation is best reserved for the biological setting, as the clinical impact is likely different depending on the scenario. If an iatrogenic full thickness tumor defect arises whilst the specimen is in situ within the abdominal cavity, there is likely some risk of tumor seeding the peritoneal cavity and we consider this is best regarded as pT4a disease. This interpretation is however offered without good evidence. In contrast, if such an iatrogenic defect occurs once the specimen is outside the abdominal cavity, this should not influence pT classification. Interpretation therefore requires close clinicopathological correlation and this should always be explained in the pathology report.

## Relation of tumor to anterior peritoneal reflection
For rectal cancers, the relationship of the tumor to the anterior peritoneal reflection is reported as a core item, as this predicts the risk of local recurrence in addition to peritoneal recurrence [fig_ref] FIGURE 2: Rectal anatomy and possible relationships of rectal cancers to the peritoneal reflection [/fig_ref]. 14 The anterior aspect of the rectum has a peritoneal covering to the level of the peritoneal reflection. Posteriorly, the nonperitonealized margin is represented by a triangular-shaped bare which extends superiorly in continuity with the mesentery of the sigmoid colon.

## Plane of mesorectal excision
Prospective randomized controlled trials have demonstrated that, in patients with rectal cancer, use of total mesorectal excision (TME) surgery improves local recurrence rates and the survival by up to 20%. [bib_ref] Local recurrence following total mesorectal excision for rectal cancer, Arbman [/bib_ref] [bib_ref] Preoperative radiotherapy combined with total mesorectal excision for resectable rectal cancer, Kapiteijn [/bib_ref] Furthermore, objective macroscopic assessment by pathologists of the surgical plane of excision predicts margin involvement, local recurrence and survival. [bib_ref] Effect of the plane of surgery achieved on local recurrence in patients..., Quirke [/bib_ref] [bib_ref] Macroscopic evaluation of rectal cancer resection specimen: clinical significance of the pathologist..., Nagtegaal [/bib_ref] This grading is therefore considered a core item for reporting. The optimal plane is that of the mesorectal fascia (complete TME) whilst excision extending onto the muscularis propria (incomplete TME) is associated with the worst outcomes. Overall macroscopic assessment of the intact specimen, with grading based on the worst area, is as described in [fig_ref] TABLE 2: Pathological Assessment of Rectal and Colonic Cancer Surgical Resection Specimens [/fig_ref] and illustrated in [fig_ref] FIGURE 3: Planes of colorectal cancer surgery for the mesorectum [/fig_ref].

## Plane of sphincter excision
In considering management of rectal cancer, abdominoperineal excision for lower tumors has been associated with poorer outcomes compared to anterior resection for higher tumors, due to increased rates of circumferential resection margin (CRM) involvement and intraoperative full thickness defects, referred to as perforation in this literature. [bib_ref] The abdominoperineal resection itself is associated with an adverse outcome: the European..., Den Dulk [/bib_ref] More radical surgery to remove more tissue around low rectal tumors by en bloc resection of the levator muscles, extralevator abdominoperineal excision, reduces the risk of CRM involvement and intraoperative full thickness defects leading to better long term outcomes. [bib_ref] Extended abdominoperineal excision vs. standard abdominoperineal excision in rectal cancer-a systematic overview, Stelzner [/bib_ref] [bib_ref] Multicentre experience with extralevator abdominoperineal excision for low rectal cancer, West [/bib_ref] Using staging magnetic resonance imaging (MRI), radiologists are able to predict the optimal dissection plane for abdominoperineal excision surgery. [bib_ref] Prospective validation of a low rectal cancer magnetic resonance imaging staging system..., Battersby [/bib_ref] Subsequent correlation with pathological assessment of the intact surgical excision specimen allows surgical audit of the plane of dissection achieved around the sphincters. As this assessment is currently a core data item in only 1 national CRC dataset,and not in routine use in many other countries, it has been included as a noncore item. The overall assessment is based on the worst area, as described in [fig_ref] TABLE 2: Pathological Assessment of Rectal and Colonic Cancer Surgical Resection Specimens [/fig_ref] and illustrated in [fig_ref] FIGURE 3: Planes of colorectal cancer surgery for the mesorectum [/fig_ref]. [bib_ref] Low rectal cancer: a call for a change of approach in abdominoperineal..., Nagtegaal [/bib_ref] This grading should be performed in addition to mesorectal grading for abdominoperineal excision specimens.

## Plane of mesocolic excision
Beyond assessment of rectal cancer surgery, the quality of surgical technique for colonic cancer, evaluating the plane of mesocolic excision, has been shown, in retrospective observational studies and 1 randomized clinical trial, to predict outcomes. [bib_ref] Pathology grading of colon cancer surgical resection and its association with survival:..., West [/bib_ref] Surgery in the mesocolic plane is associated with a lower rate of local recurrence and better survival when compared to surgery in the muscularis propria plane. Complete mesocolic excision, where surgery occurs in the mesocolic plane with a high vascular ligation, is associated with better plane of surgery and higher lymph node yield, although the effect of the high ligation on long term outcomes is uncertain and subject to further study. [bib_ref] Surgery along the embryological planes for colon cancer: a systematic review of..., Gouvas [/bib_ref] Pathological evaluation of mesocolic surgery is considered a non-core data item, as its application requires further validation in clinical practice. Overall assessment is based on the worst area, as described in [fig_ref] TABLE 2: Pathological Assessment of Rectal and Colonic Cancer Surgical Resection Specimens [/fig_ref] and illustrated in [fig_ref] FIGURE 3: Planes of colorectal cancer surgery for the mesorectum [/fig_ref]. 22

## Histological tumor type
The WHO Classification of Tumors of the Digestive System is recommended for tumor typing as a core item. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] Almost all CRC are adenocarcinomas, most of which are of no specific type or ''not otherwise specified'' (NOS). Specific subtypes of adenocarcinoma are recognized and defined as follows:
Mucinous adenocarcinoma has >50% of the tumor comprised of pools of extracellular Mucin, containing malignant glands, or individual tumor cells. Microsatellite instability is more common, as is the presence of an activating BRAF V600E mutation.
Signet-ring cell adenocarcinoma has >50% of the tumor demonstrating signet-ring cell morphology, in the form of malignant cells with intracytoplasmic mucin, displacing and typically indenting the nuclei. Signet-ring cell adenocarcinoma is associated with worse stage-for-stage survival relative to conventional adenocarcinoma. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] Like mucinous adenocarcinoma, there is a strong association with microsatellite instability and BRAF V600E mutation. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] Medullary carcinoma demonstrates solid sheets of malignant cells with indistinct cell boundaries, vesicular nuclei, prominent nucleoli, abundant eosinophilic cytoplasm, and prominent intratumoral and peritumoral inflammatory infiltrates. Almost invariably these tumors demonstrate microsatellite instability and are associated with a good prognosis. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] Serrated adenocarcinoma by definition demonstrates glandular serrations, often slit-like, and tumor cells usually have low nuclear to cytoplasmic ratio with abundant eosinophilic or clear cytoplasm and sometimes accompanied by areas of mucinous differentiation. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] BRAF or KRAS activating mutations are common. For the mesorectum, applicable to all rectal cancer specimens, the planes include the mesorectal plane, with intact mesorectum (A), intramesorectal plane, with mesorectal defect (B) and muscularis propria plane, with little bulk to mesorectum and exposure of muscularis propria (C). For the sphincters, applicable to all abdominoperineal excisions in addition to the mesorectal plane, the planes include the extralevator plane (D), sphincteric plane (E) and intrasphincteric plane (F). The extralevator specimen includes en bloc resection of the levator ani muscles and coccyx thus preventing the creating of a surgical waist (D). The intrasphincteric plane specimen includes a large anterior perforation (F). For the mesocolon, applicable to all colon cancer specimens, the planes include the mesocolic plane, with intact mesocolon (G), intramesocolic plane, with mesocolic defect (H) and muscularis propria plane, with ragged mesocolon and exposure of muscularis propria (I). Micropapillary adenocarcinoma is characterized by small, rounded clusters of tumor cells lying within stromal spaces mimicking vascular channels. At least 5% of the tumor should demonstrate this feature for this classification. There is an association with adverse pathological features including extramural venous invasion and lymph node metastatic disease. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] Adenoma-like adenocarcinoma is a subtype of adenocarcinoma in which at least 50% of the invasive tumor has an adenomalike appearance with villous architecture, low-grade cytology, a pushing growth pattern, and minimal desmoplastic stromal reaction. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] Demonstration of invasion is difficult on endoscopic biopsy. This subtype is associated with a good prognosis.
Neuroendocrine neoplasms of the gastrointestinal tract are currently classified into NETs, NECs and MiNENs. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] The term MiNEN incorporates the previous term mixed adenoneuroendocrine carcinoma (MANEC), in recognition that occasionally the non-neuroendocrine component of mixed tumors may not be an adenocarcinoma. NETs are now graded 1 to 3 on the basis of mitotic count and Ki-67 proliferation index, with NET grade 3 recognizing a subset of tumors previously meeting criteria for NEC, but found to be less responsive to platinumbased chemotherapy, yet have better survival compared to other NECs. [bib_ref] Gastroenteropancreatic high-grade neuroendocrine carcinoma, Sorbye [/bib_ref] Grade 3 NETs are better differentiated than NECs and the primary distinction is morphological. MiNENs are usually composed of a poorly differentiated NEC component and a conventional adenocarcinoma NOS component and each should arbitrarily constitute 30% of the tumor for this designation. This dataset is applicable to NECs and MiNENs but, given different staging and grading systems applied, NETs should not be reported using this dataset.
Other epithelial tumors rarely encountered include adenosquamous carcinoma, carcinoma with sarcomatoid components, undifferentiated carcinoma, squamous cell carcinoma, and non-signetring cell poorly cohesive adenocarcinoma.

## Histological tumor grade
Although subject to poor interobserver agreement, [bib_ref] Interobserver agreement in grading of colorectal cancers-findings from a nationwide web-based survey..., Chandler [/bib_ref] histological grade of CRC, based on gland formation, is an independent prognostic factor and is a core item. 26,27 A 2-tiered grading system is more reproducible and favored over a 4-tiered grading system. Aligning with the latest WHO classification, 2 grading is based on the least differentiated component, rather than predominant pattern, although this is recommended without good evidence and a minimum area of high-grade tumor required for classification as highgrade has not been defined. Tumor buds or poorly differentiated clusters, most commonly seen at the invasive front, should not be considered in the evaluation of grade. Grading based on poorly differentiated clusters may be superior to conventional grading with respect to both prognostic value and reproducibility but further studies are required in this regard. [bib_ref] Poorly differentiated clusters predict colon cancer recurrence: an in-depth comparative analysis of..., Konishi [/bib_ref] According to the latest WHO classification, only adenocarcinoma NOS and mucinous adenocarcinoma should be graded. [bib_ref] Tumours of the colon and rectum, Nagtegaal [/bib_ref] Grading is not applicable to other subtypes of adenocarcinoma, as assessment of gland formation is difficult to apply to subtypes and most subtypes are associated with their own clinical prognosis independent of grade. Mucinous adenocarcinoma should be graded on glandular formation and epithelial maturation. 2

## Extent of invasion
Local invasion depth of CRC is categorized by the pT classification. This is the most important prognostic factor in CRC and is a core data item, using UICC and AJCC 8th edition criteria.The only exception is that pT in situ is not recognized in this dataset. This is somewhat contentious and rare cases of colorectal neoplasia confined to invasion of the lamina propria (intramucosal invasive neoplasia or intramucosal carcinoma) are acknowledged but, given the negligible metastatic potential of such neoplasms, [bib_ref] Intramucosal colorectal carcinoma with invasion of the lamina propria: a study by..., Kojima [/bib_ref] the consensus position of the DAC was that these should be classified under the same category as high grade dysplasia/high grade noninvasive neoplasia.
Given the clear anatomical delineation of the muscularis propria at most sites, defining pT1-pT3 tumors, classification of this extent of invasion is not often problematic. An exception is the low rectum, where complexities of sphincter anatomy make accurate assessment of level of invasion challenging. The internal sphincter represents a continuation of the muscularis propria and invasion of this also constitutes pT2. Skeletal muscle fibers can cross-over from external to internal sphincter and therefore invasion of skeletal muscles fibers may only represent pT2 disease if these fibers are from the internal sphincter. Invasion beyond internal sphincter into the intrasphincteric plane, but not involving the external sphincter, is considered pT3. Note that in some areas of the sphincter complex the internal and external sphincter muscles are directly apposed with only a theoretical space between.
pT4 includes tumor infiltration of the peritoneal surface (pT4a) or involvement of an adjacent organ or structure (pT4b). Peritoneal involvement has been demonstrated by multivariate analysis to have a negative impact on prognosis. [bib_ref] The prognostic importance of peritoneal involvement in colonic cancer: a prospective evaluation, Shepherd [/bib_ref] Data from a cohort of >100,000 colon cancer cases indicate that pT4a carcinomas have on average a 10% to 20% better 5-year survival than pT4b carcinomas for each pN category. [bib_ref] Revised TN categorization for colon cancer based on national survival outcomes data, Gunderson [/bib_ref] Involvement of the peritoneal surface requires tumor breaching the serosa with tumor cells visible either on the peritoneal surface, free in the peritoneal cavity or separated from the peritoneal surface by inflammatory cells only. [bib_ref] Identification of objective pathological prognostic determinants and models of prognosis in Dukes'..., Petersen [/bib_ref] If tumor passes close to the serosal surface and elicits a mesothelial reaction without clear invasion, this is categorized as pT3, although additional sections and/or multiple levels should be examined to look deeper invasion. This setting is prone to interobserver variation however. [bib_ref] Wide variability in assessment and reporting of colorectal cancer specimens among North..., Kirsch [/bib_ref] Elastic stains to identify peritoneal elastic lamina invasion are advocated in some studies, as a staging or prognostic tool. [bib_ref] Peritoneal elastic laminal invasion of colorectal cancer: the diagnostic utility and clinicopathologic..., Kojima [/bib_ref] [bib_ref] Peritoneal elastic lamina invasion in colorectal cancer: the answer to a controversial..., Puppa [/bib_ref] Cases with tumor perforation are classified as pT4a, without the need to document tumor cells on the peritoneal surface.
It is important to distinguish peritoneal involvement through direct continuity with the primary tumor from discontinuous peritoneal deposition. The former indicates pT4a disease, whereas the latter is regarded as distant metastatic disease, pM1c. It is also important to distinguish involvement of a peritoneal surface from involvement of a nonperitonealized resection margin. Peritoneal involvement is a risk factor for peritoneal metastases whilst margin involvement is a risk factor for local recurrence.
Adjacent organ involvement by tumor (pT4b) may follow peritoneal invasion or, for example in low rectal tumors, represent direct extraperitoneal invasion. If a tumor is macroscopically adherent to another organ, microscopic invasion must be demonstrated to classify as pT4b; otherwise, the adherence is considered inflammatory in nature. Longitudinal tumor extension into the wall of an adjacent segment of the intestine does not influence pT classification. Rectal tumors invading skeletal muscle of the external sphincter and/ or levator ani are classified as pT4b.

## Measurement of invasion beyond muscularis propria
Prognosis of patients with pT3 tumors can be stratified accordingly to their extent of invasion of the primary tumor beyond the muscularis propria, with !5 mm an accepted cut-off for higher risk in some studies. [bib_ref] Intramucosal colorectal carcinoma with invasion of the lamina propria: a study by..., Kojima [/bib_ref] Based on the level of existing evidence, this is considered a non-core item for reporting. The distance beyond the muscularis propria is measured to the nearest mm from the outer margin of the muscularis propria. In the event of local tissue destruction by tumor, reconstruction of this outer margin may be required for the purposes of measurement. The measurement should be performed macroscopically and refined microscopically if appropriate.

## Lymphatic and venous invasion
The presence or absence of lymphovascular invasion has strong prognostic implications for CRC and this should be reported as a core item. Classification is required according to the type of vessels involved [fig_ref] FIGURE 4: Metastatic pathways in colorectal cancer [/fig_ref] and, for veins, their intramural or extramural location, as the vessel type and location have different clinical and prognostic implications. Extramural venous invasion, present beyond the muscularis propria, has the greatest clinical significance, having been demonstrated on multivariate analysis in multiple studies to be a stage-independent adverse prognostic factor. [bib_ref] Multivariate analysis of prognostic factors for operable rectal cancer, Freedman [/bib_ref] Intramural venous invasion, identified within the submucosa or muscularis propria but not beyond, is also of prognostic importance but the evidence is much weaker than for extramural venous invasion. [bib_ref] Identification of objective pathological prognostic determinants and models of prognosis in Dukes'..., Petersen [/bib_ref] [bib_ref] Intramural and extramural vascular invasion in colorectal cancer: prognostic significance and quality..., Betge [/bib_ref] [bib_ref] The value of intramural vascular invasion in colorectal cancer-a systematic review and..., Knijn [/bib_ref] The minimum criteria for calling venous invasion are debatable. The longstanding definition of [bib_ref] Invasion of veins by carcinoma of rectum: method of detection, histological features..., Talbot [/bib_ref] is approved, whereby venous invasion is defined as tumor present within an endothelium-lined space that is either surrounded by a rim of muscle or contains red blood cells. [bib_ref] Invasion of veins by carcinoma of rectum: method of detection, histological features..., Talbot [/bib_ref] Proximity of a rounded or elongated deposit of tumor beside an artery should raise suspicion of venous invasion but is not diagnostic without identification of a residual venous wall. Examination of further levels and additional stains may help interpretation. [bib_ref] Use of an elastic stain to show venous invasion in colorectal carcinoma:..., Howlett [/bib_ref] [bib_ref] Venous invasion in colorectal cancer: impact of an elastin stain on detection..., Kirsch [/bib_ref] A circumscribed tumor nodule surrounded by a smooth muscle wall or an identifiable elastic lamina is considered sufficient to classify as venous invasion.
Small vessel invasion is defined as involvement of thin-walled structures lined by endothelium, without an identifiable smooth muscle layer or elastic lamina. Small vessels may represent lymphatics, capillaries or post-capillary venules, and invasion of these should be distinguished from large vessel (venous) invasion. D2-40 immunohistochemistry, which only stains lymphatic endothelial cells, not venular, can be used to classify small vessel invasion further but this is not in routine use in this setting. Small vessel invasion of all forms is considered under the ''L'' classification under UICC/AJCC TNM 8th editions.The identification of small vessel invasion has been reported in some but not all studies to be associated with lymph node metastatic disease and represent an independent prognostic factor. [bib_ref] Intramural and extramural vascular invasion in colorectal cancer: prognostic significance and quality..., Betge [/bib_ref] [bib_ref] Clinicopathological risk factors of Stage II colon cancer: results of a prospective..., Santos [/bib_ref] [bib_ref] Prognostic significance of lymphovascular invasion in sporadic colorectal cancer, Lim [/bib_ref] [bib_ref] The detection and role of lymphatic and blood vessel invasion in predicting..., Van Wyk [/bib_ref] The relative importance of intramural and extramural anatomic location with respect to small vessel invasion has not been well established. [bib_ref] Intramural and extramural vascular invasion in colorectal cancer: prognostic significance and quality..., Betge [/bib_ref] 

## Perineural invasion
The presence of perineural invasion in CRC [fig_ref] FIGURE 4: Metastatic pathways in colorectal cancer [/fig_ref] has adverse prognostic implication, particularly in stage II disease. [bib_ref] Clinicopathological risk factors of Stage II colon cancer: results of a prospective..., Santos [/bib_ref] [bib_ref] Characterization of perineural invasion as a component of colorectal cancer staging, Ueno [/bib_ref] [bib_ref] Perineural invasion is a strong prognostic factor in colorectal cancer: a systematic..., Knijn [/bib_ref] Although the importance of anatomic location in perineural invasion is not well established, 1 large multicenter study, reported adverse prognostic significance for both intramural and extramural locations. [bib_ref] Characterization of perineural invasion as a component of colorectal cancer staging, Ueno [/bib_ref] The presence or absence of any perineural invasion is therefore considered a core item but it is not necessary to specify anatomical location.

## Lymph node status
Regional lymph node status determines the need for adjuvant chemotherapy and is a core item. Nonregional lymph node involvement is distant metastatic (pM1) disease. If a specimen contains synchronous primary tumors in distinct anatomic regions, attempt should be made to assign lymph nodes by regional status and each cancer assessed for nodal status separately.
It is important to perform a diligent pathological dissection to identify all lymph nodes in a specimen as lymph nodes containing metastatic disease may be very small. Individual dissectors and departments should aim for a median lymph node yield of at least 12 per case. Low lymph node harvest is an adverse prognostic factor in stage II disease. [bib_ref] Lymph node evaluation and survival after curative resection of colon cancer: systematic..., Chang [/bib_ref] This reflects a combination of inadequate nodal retrieval and unfavorable patient immunology.
Micrometastases (size between 0.2 mm and 2 mm) are associated with recurrence in stage I/II CRC compared to tumor-negative nodes, but there is no increased risk of disease recurrence in the presence of ''isolated tumor cells'' (single tumor cells or groups <0.2 mm in maximum dimension) compared to tumor-negative nodes. [bib_ref] The prognostic value of micrometastases and isolated tumour cells in histologically negative..., Sloothaak [/bib_ref] Therefore, any lymph nodes containing micrometastatic or larger tumor foci are considered as positive nodes whereas isolated tumor cells, identified on H&E or immunohistochemical staining, when representing the only form of nodal involvement should be classified as pN0, with a comment indicating the presence of isolated tumor cells and optional designation as pN0(i).
Following neoadjuvant therapy, only the identification of viable tumor constitutes nodal involvement (ypN1/2). Necrosis, fibrosis or acellular mucin within lymph nodes in this setting is not considered nodal tumor involvement. Nevertheless, a descriptive comment of these findings indicates likely response to therapy and allows correlation with initial staging MRI.

## Tumor deposits
The term tumor deposit, or satellite, was introduced in the UICC/AJCC TNM 7th editionsand the concept refined in UICC/ AJCC TNM 8th editions: discrete macroscopic or microscopic nodules of cancer in the pericolorectal adipose tissue's lymph drainage area of a primary carcinoma that are discontinuous from the primary and without histological evidence of residual lymph node or identifiable vascular or neural structures [fig_ref] FIGURE 4: Metastatic pathways in colorectal cancer [/fig_ref].If a vessel wall is identifiable on H&E, elastic or other stains, it should be classified as venous invasion or lymphatic invasion and if neural structures are identifiable in association with the tumor, the lesion should be classified as perineural invasion rather than as a tumor deposit. A minimum size of deposit or minimum distance of separation from the primary tumor, or further other deposits, is not specified. Neither is guidance on how to classify mesenteric tumor which demonstrates lymphatic, venous or perineural invasion, but where the bulk of the tumor appears unrelated to the vascular or neural structure. The identification of a tumor deposit is considered under the node (N) rather than primary tumor (T) status for the purposes of staging and tumor deposits in the absence of lymph node metastases are classified as pN1c. In the presence of lymph node metastases, tumor deposits are discounted for staging purposes. However, there is evidence from meta-analysis of the adverse prognostic significance of tumor deposits in the presence of lymph node metastatic disease, based on the UICC/AJCC TNM 7th editions 48,49 definition, and therefore the presence and number of identified tumor deposits should be recorded in all cases, as a core item. [bib_ref] Tumor deposits in colorectal cancer: improving the value of modern staging-a systematic..., Nagtegaal [/bib_ref] Mesenteric tumor, without evidence of origin, which is discontinuous from the primary tumor and predominantly subserosal in location but which penetrates the serosal surface of the mesentery, should be classified as a tumor deposit rather than as distant metastatic (pM1c) disease. This does not influence the pT category, which should be based on extent of local invasion of the primary tumor only. However, given serosal involvement by the tumor deposit may equate clinically to pT4a disease, a comment may be usefully added to this effect. Guidance on this interpretation is offered without good evidence. pM1c disease should be reserved for cases where the tumor appears to have arisen from metastatic spread via the peritoneal cavity.
In the setting of tumor regression following administration of neoadjuvant therapy, the distinction of discontinuous residual primary tumor foci from tumor deposit is difficult and subjective. To facilitate uniform interpretation, it is recommended that designation as tumor deposit should necessitate the presence of intervening normal tissue, rather than just fibrosis or acellular mucin. . B, Lymph node metastatic disease (white arrows) and EMVI (black arrow,) confirmed by identification of an elastic lamina in the vein wall (inset) on histochemical staining (H&E, elastic van gieson). C, Lymphatic invasion, malignant glands (arrow) lying within a thin-walled lymphatic channel, surrounded by lymphoid cells (H&E). D, Perineural invasion, malignant glands infiltrating thickened neural bundles (arrows), highlighted by S100 immunohistochemical staining (Upper, H&E; Lower, S100). E indicates tumor deposit, defined by the absence of features of any identifiable metastatic pathway (ancillary stains noncontributory).

## Tumor budding
There is considerable interest in tumor budding, considered to be a morphological manifestation of epithelial mesenchymal transition. [bib_ref] Epithelial mesenchymal transition and tumor budding in aggressive colorectal cancer: tumor budding..., Zlobec [/bib_ref] A tumor bud is defined as a single tumor cell or cluster of up to 4 tumor cells at the invasive front of carcinomas. Budding is of potential clinical relevance to CRC in 2 distinct settings. First, multiple studies have shown that pT1 CRC with greater budding (tumor budding scores Bd2 and Bd3) are associated with an increased risk of lymph node metastatic disease compared to those with lesser budding (tumor budding score Bd1). [bib_ref] Systematic review and meta-analysis of histopathological factors influencing the risk of lymph..., Beaton [/bib_ref] [bib_ref] Predicting lymph node metastasis in pT1 colorectal cancer: a systematic review of..., Bosch [/bib_ref] [bib_ref] Tumor budding as a risk factor for nodal metastasis in pT1 colorectal..., Cappellesso [/bib_ref] Second, in stage II CRC, tumor budding score Bd3 is associated with an increased risk of recurrence and mortality. [bib_ref] The role of tumour budding in predicting survival in patients with primary..., Van Wyk [/bib_ref] As recommended from the International Tumor Budding Consensus Conference (ITBCC) of 2016, 56 tumor budding is scored using a 3-tier system according to the number of buds evident in the highest count after scanning 10 separate fields (at 20A objective lens) along the invasive front of the tumor or the entire lesion for malignant polyps (''hotspot'' approach). The number of tumor buds is based on haematoxylin and eosin (H&E) assessment, although pan-cytokeratin immunohistochemistry can be used to help identify hotspots. [bib_ref] Cytokeratin-based assessment of tumour budding in colorectal cancer: analysis in stage II..., Koelzer [/bib_ref] This may be of particular value when the invasive front is obscured by inflammatory cells. A correction for microscope eyepiece field diameter is required, the bud count normalized to a field area of 0.785 mm 2 (equivalent to an objective lens 20A with eyepiece diameter of 20 mm).
Tumor budding, applying the above system to assess tumor budding score (Bd1-Bd3) and actual number of buds, is considered a non-core item for reporting, pending the emergence of further evidence of reproducibility of assessment and clinical significance. Note that budding should only be reported in nonmucinous and nonsignet-ring cell adenocarcinoma areas of tumor and budding should not be reported in cancers resected after neoadjuvant therapy.

## Response to neoadjuvant therapy
Any form of neoadjuvant therapy may result in morphological tumor response in the form of fibrosis, necrosis or acellular mucin. The presence of complete or marked tumor regression in rectal cancer resection specimen is associated with a better outcome. [bib_ref] Long-term outcome in patients with a pathological complete response after chemoradiation for..., Maas [/bib_ref] [bib_ref] Prognostic significance of tumor regression after preoperative chemoradiotherapy for rectal cancer, Rodel [/bib_ref] For grading of regression, a 4-tier system is recommended, based on a modification of the system described by This is a core item for reporting. Assessment of regression is based on evaluation of the primary tumor site. Similar features may be evident within regional lymph nodes involved by metastatic tumor, or at any distant metastatic sites. Although findings at metastatic sites do not influence tumor regression score, a descriptive comment in the pathology report is recommended to allow correlation with imaging. Overall designation as a complete pathological response requires the absence of viable tumor locally (ypT0) and in lymph nodes (ypN0). The entire tumor bed should be processed for histological examination in this situation.

## Margin status
Assessment of surgical margin status is a core item. In particular, circumferential or nonperitonealized margin involvement in rectal cancer is strongly predictive of local recurrence and poor survival. [bib_ref] What is the role for the circumferential margin in the modern treatment..., Nagtegaal [/bib_ref] [bib_ref] Rates of circumferential resection margin involvement vary between surgeons and predict outcomes..., Birbeck [/bib_ref] Margin involvement in colon cancer is much less common and there is less evidence of its significance. [bib_ref] Retroperitoneal margin involvement by adenocarcinoma of the caecum and ascending colon: what..., Scott [/bib_ref] [bib_ref] The retroperitoneal surface in distal caecal and proximal ascending colon carcinoma: the..., Bateman [/bib_ref] The definition of margin involvement is somewhat contentious but it is generally accepted that any circumferential margin 1 mm should be regarded as involved. The precise distance to the margin should be recorded, to the nearest 0.1 mm, if less than 1 mm, and to the nearest 1 mm, if <10 mm. This assessment may require a combination of macroscopic and microscopic evaluation. Any separately submitted anastomotic rings should be taken into consideration in measuring the distance to longitudinal margins.
There is some evidence to suggest that margin involvement due to discontinuous or intravascular tumor is associated with a similar risk of local recurrence to that of margin involvement by primary tumor. [bib_ref] What is the role for the circumferential margin in the modern treatment..., Nagtegaal [/bib_ref] [bib_ref] Rates of circumferential resection margin involvement vary between surgeons and predict outcomes..., Birbeck [/bib_ref] Margin involvement by tumor within a lymph node, however, was reported in 1 study not to be associated with a significant risk of local recurrence. [bib_ref] Rates of circumferential resection margin involvement vary between surgeons and predict outcomes..., Birbeck [/bib_ref] Therefore, if a lymph node containing tumor is present at the resection margin, and the lymph node capsule is intact, the circumferential margin should not be reported as involved . A comment should be added to the FIGURE 5. A, Posterior aspect of a right hemicolectomy specimen highlighting an intact, enlarged lymph node (rectangle) abutting the posterior specimen margin. B, Histology of a horizontal section through this lymph node shows metastatic mucinous adenocarcinoma. Although tumor extends to the surgical margin (painted black at base of image), tumor is confined to the intact lymph node and therefore NOT considered to represent margin involvement.
pathology report describing the interpretation. In the setting of margin involvement by discontinuous tumor, this should be clearly reported and a separate measurement provided of distance from the primary tumor.

## Coexistent pathology
Any background colonic or rectal pathological abnormalities, such as polyps, chronic inflammatory bowel disease, effects of neoadjuvant therapy, diverticular disease, or obstructive changes should be recorded as non-core information. In the event of !2 synchronous primary carcinomas, individual datasets should be completed as appropriate.

## Ancillary studies
Clinical applications of ancillary testing applied to CRC are limited but expanding. Reflex testing for defective mismatch repair (MMR)/microsatellite instability (MSI) status is now widely recommended for the detection of Lynch syndrome, 65,66 caused by either a constitutional pathogenic mutation in one of the MMR genes, or sporadic MMR deficient CRC, usually caused by hypermethylation of the MLH1 MMR gene promoter region. Defective MMR (dMMR) associated with MLH1 loss, or a MSI-high result, triggers algorithmic testing, including somatic BRAF mutation testing and/or MLH1 promoter methylation testing, to distinguish between sporadic dMMR cancers and Lynch syndrome. Absence of BRAF V600 mutation and/or absent MLH1 promoter hypermethylation should prompt a recommendation of referral to clinical genetics for appropriate counseling before germline mutation screening of the relevant MMR genes, as should loss of PMS2, MSH2, and/or MSH6 immunohistochemical expression. MMR status also informs patient management with MMR deficiency associated with good prognosis, poorer response to 5-fluorouracil-based chemotherapy and potential response to immune checkpoint blockade therapy. [bib_ref] Mismatch repair deficiency predicts response of solid tumors to PD-1 blockade, Le [/bib_ref] Patients with metastatic CRC should be tested for RAS (KRAS and NRAS) and BRAF mutations when treatment with anti-epidermal growth factor receptor (anti-EGFR) therapy is considered.Similarly, it is likely that the presence of the V600E BRAF mutation confers resistance to anti-EGFR therapy, though this may be modified by addition of a BRAF and/or MEK inhibitor. [bib_ref] Predictive role of BRAF mutations in patients with advanced colorectal cancer receiving..., Pietrantonio [/bib_ref] [bib_ref] Improvements in clinical outcomes for BRAF(V600E)-mutant metastatic colorectal cancer, Morris [/bib_ref] Most modern guidelines therefore recommend also testing metastatic CRC for the V600E BRAF mutation.Although the above indications for focused ancillary testing are now well established, facilities for such testing are not globally available. As such, these are currently considered non-core items for reporting. It is inevitable that further clinical applications of ancillary testing will emerge and this will be kept under review.

## Histologically confirmed distant metastases
It is occasionally possible to designate a case as having histologically confirmed distant metastatic disease (pM1) on examination of either the main surgical resection specimen, for example when a peritoneal or omental deposit is identified, or of a separately submitted biopsy or resection specimen, for example from the liver or a nonregional lymph node.
UICC/AJCC 8th edition staging systems recognize prognostic stratification according to the pattern of organ involvement by distant metastatic disease and have subclassified pM1 into pM1a indicating metastatic disease in 1 distant organ (excluding metastatic peritoneal disease), pM1b indicating metastatic disease in !2 distant organs and pM1c indicating metastatic peritoneal disease (regardless of other organ involvement).It is therefore important for pathologists to accurately document such disease and this is considered a core item for reporting. It should be noted that pathologists can only make a positive statement regarding distant metastatic disease, their assessment based on selected specimens submitted to them for examination, and therefore the terms ''pM0'' or ''pMX'' should no longer be used. cM1 and cM0 can be applied according to best radiological and intraoperative evidence available.

## Pathological staging
The agreed criteria of the UICC and AJCC 8th editions are applied to derive TNM stage.The only exception is that this dataset does not advocate the use of pT in situ, as discussed above.
If completion surgery follows a diagnosis of carcinoma made in a local excision specimen, the pathological findings within both specimens should be considered in providing a single, overall TNM stage. Similarly, if a resection specimen contains synchronous primary carcinomas, each should be separately assessed and individual datasets completed, but a single overarching stage provided, following the conventions of TNM.

# Discussion
Quality of pathology reporting and mutual understanding between colorectal surgeon and pathologist is vital to management and outcomes of CRC patients. It is well established that adoption of structured pathology reporting is associated with greater clinician satisfaction and improved access to pathology information relevant to patient management, as well as ease of returning pathology data for central registration purposes. [bib_ref] Standardized synoptic cancer pathology reports -so what and who cares? A population-based..., Lankshear [/bib_ref] [bib_ref] Standardized synoptic cancer pathology reporting: a population-based approach, Srigley [/bib_ref] Adoption of structured reporting helps ensure data is complete and it has been demonstrated for CRC to reduce the risk of missing assessment of important pathology features when compared to narrative reporting, especially for nonspecialist pathologists, thereby impacting patient care. [bib_ref] Standardized synoptic cancer pathology reporting: a population-based approach, Srigley [/bib_ref] [bib_ref] What impact has the introduction of a synoptic report for rectal cancer..., Messenger [/bib_ref] [bib_ref] Improvement of care in patients with colorectal cancer: influence of the introduction..., Sluijter [/bib_ref] There remains an important role, however, for a narrative component to pathology reports, explaining any areas of uncertainty or unusual pathological findings which may be pertinent to individual patient management and offer useful feedback to the surgeon.
Herein we have described the process of creation of such a dataset for CRC surgical resection specimens, involving an international panel of expert gastrointestinal pathologists from 9 countries and with representation from colorectal surgery and oncology. There was strong representation of authors of equivalent existing CRC datasets from the US, UK, and Australasia. A key aim of ICCR is to minimize the workload involved in production and regular update of such datasets in addition to standardization of reporting to facilitate international comparisons. Scrutiny of these existing national datasets illustrates the current problem of lack of uniformity.Although most of the content is uniform between datasets, there are subtle but important differences pertaining to numerous data items, which would hinder comparison. This is the first agreed international dataset for CRC pathology reporting. It is hoped that the various national datasets align with this ICCR version in the future. This dataset is more extensive than the UICC/AJCC TNM cancer staging systems, which provide primarily a classification of anatomical extent of disease and represent the most powerful predictor of clinical outcome for many cancers. Incorporation of additional prognostically relevant morphological features into TNM staging is challenging. Some, specifically venous, lymphatic, and perineural invasion, can already be optionally recorded under the UICC/AJCC systems, not impacting the summary stage. However, as a result the prognostic impact of these features may not be fully considered in the clinical management of individual cases. More prominent integration of newly defined prognostic features into the TNM system will be complex, for example as described above for tumor deposits. Nevertheless, international discussion of such features is necessary to further the goals of reproducible consensus definitions and standardization of interpretation.
The ICCR aspires to widespread uptake of this freely available dataset by those countries currently lacking such a strategy, to improve the standard of pathology reporting of CRC globally. The greatest effect may be in low-and middle-income countries, where incidence of CRC has risen significantly. [bib_ref] Global burden of 5 major types of gastrointestinal cancer, Arnold [/bib_ref] Standardized reporting will allow comparison of relative proportions of CRC subtypes between countries, assessment of the impact of new screening programs and participation in international trials targeting a specific molecular subset of CRC and requiring a minimum standard of pathology reporting.
To conclude, this internationally agreed freely available dataset provides a structured template for the pathological reporting of CRC surgical resection specimens. The ICCR initiative streamlines the dataset production process, both for new datasets and for regular updates as new evidence emerges. Such international collaborative efforts become more important with rapid progress in the fields of molecular pathology, digital pathology, and image analysis, allowing rapid translation of new developments, many relevant to surgical practice, into routine pathology reporting.
[fig] FIGURE 1: A fresh anterior exenteration specimen comprising abdominoperineal excision of the rectum and anus with en bloc levator ani muscles, prostate, seminal vesicles and bladder. [/fig]
[fig] FIGURE 2: Rectal anatomy and possible relationships of rectal cancers to the peritoneal reflection. Adapted by permission from Nicholas P. West and Philip Quirke: Springer Multidisciplinary Treatment of Colorectal Cancer (G. Baatrup, ed.); Quality of Surgery by Nicholas P. West and Philip Quirke (2021). [/fig]
[fig] FIGURE 3: Planes of colorectal cancer surgery for the mesorectum (A-C), sphincters (D-F) and mesocolon (G-I). [/fig]
[fig] FIGURE 4: Metastatic pathways in colorectal cancer. A, Obvious extramural venous invasion (EMVI, black arrows), including a focus extending perpendicularly from muscularis propria (white arrow) [/fig]
[table] TABLE 1: Core and Non-Core Elements for ReportingThese items are only relevant to certain specimen types-see text for details. [/table]
[table] TABLE 2: Pathological Assessment of Rectal and Colonic Cancer Surgical Resection Specimens [/table]