This policy does not designate specific special histochemical stains (aka
special stains) and/or immunohistochemical (IHC) stains that should be used in
the differential diagnosis of tissues or neoplasms because this information is
readily available in textbooks and various scientific publications. This
policy identifies the medically necessary criteria for the use of special
stains and/or IHC stains. Additionally, this policy addresses, based on claims
review, the scenarios that may be driving medically unnecessary over-
utilization or incorrect billing of these services including:

  * Reflex templates or pre-orders for special stains and/or IHC stains prior to review of the routine hematoxylin and eosin (H&E) stain by the pathologist; or
  * Use of special stains and/or IHC stains without clinical evidence that the stain is actionable or provides the treating physician with information that changes patient management; or
  * Use of added stains when the diagnosis is already known based on morphologic evaluation of the primary stain.

The surgical pathology report is expected to designate the specific block(s)
upon which IHC testing is performed, the reason and results for IHC testing,
the specific markers, and whether single antibody(ies) or a cocktail of
antibodies is utilized. A statement alone in the pathology report that states,
"IHC confirms the diagnosis" will not be covered as reasonable and necessary.

**Medical Necessity of Services Performed**  
There are many different relationships that exist in the provision of
pathology services in the United States. It is the obligation of each party to
recognize that they are responsible for the medical necessity of the services
submitted. For example, when a physician or physician group performs the
professional component of services described in this policy and another entity
performs the technical services, it is the obligation of each entity to
independently assure the medical necessity of the services rendered by each
entity.

**Special Stains/IHC Medical Necessity**

The CMS Internet-Only Manual, Pub. 100-02, Medicare Benefit Policy Manual,
Chapter 15, 80.6.5 specifies "...there may be additional tests, such as special
stains, that the pathologist may need to perform, even though they have not
been specifically requested by the treating physician/practitioner. The
pathologist may perform such additional tests under the following
circumstances:

  * Services are **medically necessary** so that a complete and accurate diagnosis can be reported to the treating physician/practitioner;
  * **Results** of the tests are communicated to and are used by the treating physician/practitioner in the treatment of the beneficiary; and
  * Pathologist **documents** in their report **why** additional testing was done."

The above citation means that reflex templates or pre-orders for special
stains and/or IHC stains prior to review of the routine H&E stain by the
pathologist are not reasonable and necessary. A pathologist must first review
the H&E stain prior to ordering special stains or IHC.

Exceptions do exist and are recognized standards of care in the practice of
pathology. These exceptions include but are not limited to renal, liver, and
neuromuscular biopsies, and for the suspicion of an infectious disease,
particularly in an immune compromised patient. In certain clearly defined
circumstances, it may be reasonable to perform some IHC on sentinel lymph
nodes when the frozen sections show they are free of tumor.

The medical necessity for the special stain or IHC studies, and the results of
the stain or IHC, must be documented in the surgical pathology report.

**IHC for Breast Pathology**

[PharmDx Ki-67 (MIB-1)](https://www.fda.gov/medical-devices/recently-approved-
devices/ki-67-ihc-mib-1-pharmdx-dako-omnis-p210026) by Agilent Technologies
has prognostic value in the population of patients with ER+, HER2- lymph node
positive high risk breast cancer for use of the Cyclin-dependent 4 and 6 (CDK
4/6) inhibitor abermaciclib (Eli Lilly and Company) as adjuvant therapy in
addition to endocrine therapy. Outside of this exception, Ki-67 is not
considered reasonable and necessary for breast cancer and consequently will
not be covered by Medicare.

In the absence of professional guidelines based on proven scientific
literature, standing orders from clinicians for such tests as Ki-67 and
epidermal growth factor receptor (EGFR) on every breast cancer are not
reasonable and necessary, and are not a covered Medicare service.

**Special Stains and/or IHC for Gastrointestinal (GI) Pathology**  
Only the pathologist may determine the medical necessity of a special stain.
Ordering special stains or IHC stains prior to review of the routine H&E stain
is not reasonable and necessary.

Other examples of special stains or IHC that are not reasonable and necessary
on every specimen include:

  * Esophagus - fungal stains, trichrome, diastase-PAS (D-PAS), CDX-2 or other mucin stains;
  * Gastric - alcian blue/periodic acid-Schiff (AB-PAS), D-PAS, CDX-2 or other mucin stains, or special stains or IHC for Helicobacter pylori (H. pylori), or neuroendocrine markers such as synaptophysin or chromogranin;
  * Duodenum - AB-PAS, D-PAS, CD3, and trichrome, or other mucin stains;
  * Colon - CD3, p53 trichrome;
  * Hyperplastic polyps - Ki-67, CK20, p53, CEA, BRAF; and
  * Tubular or tubulovillous adenoma - Ki-67, CK20, CEA, p53, mismatch repair (MMR).

If special stains or IHC are needed in addition to the routine H&E for gastric
specimens, specific documentation to justify the medical necessity for the
stain is required in the pathology report. Cases that may require special
stains or IHC include but are not limited to the following:

  * Detection of H. pylori in an appropriate milieu when organisms are not seen on H&E stained slides;
  * Evaluating atrophic gastritis for evidence of autoimmune etiology and for enterochromaffin-like (ECL) cell hyperplasia/carcinoid tumor;
  * Characterizing a carcinoma, lymphoma, melanoma or sarcoma;
  * Defining a gastrointestinal stromal tumor (GIST) and to distinguish it from mimics; and
  * Ki-67 by IHC in the differential diagnosis of certain neuroendocrine tumors of the gut.

**Special Stains and/or IHC for Prostate Pathology**

It is not reasonable and necessary to perform IHC testing (either single
antibody or antibody cocktails) on cases with morphologically negative cores.
It is not reasonable and necessary to perform IHC testing in a negative or a
suspicious core biopsy when obvious prostate cancer is present in other cores.
While the pathologist may choose to confirm a suspicious focus in 1 or more
cores in a case where the diagnosis of cancer has already been made, it is not
a Medicare covered service because it provides no additional actionable
information to the treating physician.

Prostate cases that may require reasonable and necessary IHC staining include
but are not limited to the following:

  * Indeterminate/suspicious focus and no other cores are positive for cancer;
  * Single worrisome core with minimal % tumor (roughly <5%);
  * Worrisome core(s) contralateral to a positive core(s): 
    * In a multi-part biopsy with Gleason 3+3=6 cancer in 1 part, and atypical small acinar proliferation (ASAP) suspicious for Gleason 3+3=6 cancer in other part(s); the number of positive biopsy sites and % core involvement of these sites can affect therapeutic choices for active surveillance (AS), focal therapy or surgery
    * In a multi-part biopsy with 4+3=7 or 4+4=8 cancer in 1 part, and ASAP suspicious for the same grade cancer in other part(s); workup is justified since the extent of high-grade cancer affects treatments;
  * Identify tumor invasion of adjacent structures;
  * Determine origin of undifferentiated/poorly differentiated neoplasm, such as bladder vs. prostate; and
  * Other unexpected results when specific cell stains would be necessary.

Prostate cases when IHC workup is **Not Reasonable and Necessary** include the
following:

  * In a multi-part biopsy with =3+4=7 cancer in 1 part, and ASAP suspicious for 3+3=6 cancer in other part(s), and stains are unlikely to change treatment; or
  * In a multi-part biopsy with =4+3=7 or 3+4=7 cancer in 1 part, and cribriform glands that include a differential of Intraductal Carcinoma of Prostate (ICD-P)versus invasive, Gleason pattern 4 cancer in other part(s), as intra-ductal carcinoma is almost always closely associated with invasive high-grade cancer and the results will not change the overall highest Gleason grade/Grade group for the case and may not change treatment.

**Special Stains and/or IHC for Lung Cancer**  
The diagnostic challenge of a lung biopsy can often prompt the need for
additional stains to define the neoplasm. Two important considerations need to
be considered in this regard:

  * The diagnosis of squamous cell cancer can often be made without the use of any special stains, and
  * The diagnosis of non-small cell carcinoma often requires additional stains but it is essential that tumor tissue be carefully triaged to allow the patient's sample to be tested for molecular markers (i.e., EGFR, ALK, and others) when clinically indicated.

**IHC for Predictive Marker Tumor Profiling**

Estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth
factor receptor (Her2) testing for the purpose of identifying patients likely
to respond to hormonal therapy, biologics or chemotherapy is a covered
Medicare service when medically necessary for breast and gastric
adenocarcinoma.

Chemosensitivity profile tumor panels, regardless of whether it is performed
by IHC or chromogenic in-situ hybridization (CISH), is not reasonable and
necessary and is not a Medicare covered service.

**IHC for Cervical/Gyn/Bladder/Kidney Tumors**  
A variety of IHC stains have found limited use in cervical, gynecologic, and
urologic tumor settings. In unusual cases of cervical dysplasia, markers or
surrogate markers for HPV may be useful where the diagnosis on conventional
H&E stain cannot be made with certainty. These markers are clearly not
reasonable and necessary on all biopsies.

Similarly, it is rare to need stains to prove that an endometrial or ovarian
cancer is a serous cancer or that a kidney neoplasm is an oncocytoma, an
eosinophilic or chromophobic renal cell cancer.

**IHC for Skin & Cutaneous/Soft Tissue/Central Nervous System (CNS) &
Peripheral Nervous System (PNS) Lesions**  
Most skin lesions are diagnosed with routine H&E slides. A minority of skin
lesions require immunostains (e.g., atypical fibroxanthomas, Merkel cell
lesions, lymphomas). Most common skin lesions (e.g., seborrheic keratosis) do
not require IHC stains. Use of IHC morphometric codes for skin lesions is not
reasonable and necessary.

Similarly, most soft tissue lesions do not require IHC stains or other
"special" stains.  
Many CNS and PNS lesions are readily diagnosed with routine stains. It is
unusual for a meningioma to require an IHC.

**IHC for Bone Marrow Samples**

Most bone marrow samples are diagnosed with the use of Wright's stained smears
and the use of H&E stained slides with an iron stain supplementing the
battery. The use of IHC stains may assist in the interpretation of cases where
flow cytometry (FC) does not fit with the routine slide interpretation, when
FC was not obtained or for the evaluation of cell types that are not detected
or significantly underrepresented in FC studies, such as large lymphocytes,
plasma cells and Reed-Sternberg cells. IHC stains are generally not needed to
confirm the results of FC and cytogenetic studies. When medically indicated,
justification for the use of both methods must be stated in the pathology
report and billed accordingly.

**Background**  
Routine H&E staining is the corner stone of tissue-based microscopic
diagnosis. Thin sections of tissue are stained with H&E to visualize the
tissue morphology. Hematoxylin dye stains the cell nuclei blue and the eosin
dye stains other structures pink/red. "Acid hematoxylin" is not a special
stain given that all hemotoxylin stains are acidic. This stain has never been
recognized by the Biological Stain Commission. It is not reasonable and
necessary to claim this stain as a special stain. H&E staining is included as
part of pathology services.  
  
Special stains are called "special" because they are dyes used to stain
particular tissues, structures or pathogens such as bacteria that may not be
visible by routine H&E staining. Special stains can identify whether a
substance is present or absent, where the substance is located in the tissue
specimen, and frequently, how many or how much of a substance is present.
There are special stains to identify bacteria, yeast and fungi; for connective
tissue, muscle, collagen, lipid and fibrin; for nuclei acids; and multi-
purpose stains to identify basement membranes, mucins, and various other
cellular constituents. Two major categories for special stains are recognized:
One is specifically for microorganisms; the second is for all other purposes
(not microorganisms) and specifically excludes detection of enzyme
constituents.  
  
IHC is a powerful tool for identifying substances and cells in tissue sections
using the specificity of antigen-antibody reactions, where the antibody is
linked to a colored indicator (stain) that can be seen with a microscope. More
than 400 distinct antibody targets are currently available with varying
sensitivity and specificity for a given target. A major use of IHC is to
identify poorly differentiated malignant neoplasms (tumors) such as a
carcinoma, lymphoma, melanoma and sarcoma. Some IHC stains are useful in
determining the primary site of a metastatic neoplasm, and others are used to
guide specific therapies (e.g., Her2 IHC to determine potential response to
trastuzumab).  
  
**IHC for Breast Pathology**  
The clinical care of patients with breast cancer depends upon the accurate
diagnosis and the assessment of biomarkers. Hormone receptor assays and Her2
testing are recommended on all primary **invasive** breast cancers and on
recurrent or metastatic cancers. At the current time, there is no
recommendation for Her2 testing on in situ breast lesions outside of a
clinical trial. While there are a number of promising additional biomarkers,
such as Ki-67, PI3K and gene expression assays, the College of American
Pathologists (CAP), the American Society of Clinical Oncologists (ASCO) and
the National Comprehensive Cancer Network (NCCN) have not recognized these
markers in patient treatment pathways.1-4  
  
ER, PR and HER2 are well-established prognostic markers in invasive breast
cancer management. The triple negative breast carcinoma subtype
(ER-/PR-/Her2-) has been associated with worse overall prognosis in comparison
with other subtypes in study populations consisting of ethnic minorities and
young women.1  
  
Ki-67 expression is a biomarker for proliferation and has been associated with
response to therapy, but methods of measurement are controversial. In December
2013 the CAP reported that there is "a lack of consensus on scoring,
definition of low versus high expression, an appropriate cut point for
positivity, or which part of the tumor should be scored (e.g., leading edge,
hot spots, overall average) ((CAP)). There is also paucity of data on the
effects of pre-analytical variables (e.g., ischemic time, length of fixation,
antigen retrieval) on Ki-67 staining. For these reasons, routine testing of
breast cancers for Ki-67 expression is not currently recommended by either
ASCO or the NCCN."5,6

More recent evidence identifies the use of the PharmDx Ki-67 (MIB-1) by
Agilent Technologies as a companion diagnostic test shown to define a high-
risk population along with high risk clinicopathologic features (i.e., nodal
status, tumor size, and grade). This is used to identify patients with an even
greater risk of recurrence and thus has prognostic value in the population of
patients with ER+, HER2- lymph node positive high risk breast cancer for use
of the Cyclin-dependent 4 and 6 (CDK 4/6) inhibitor abermaciclib (Eli Lilly
and Company) as adjuvant therapy in addition to endocrine therapy. With 19
months of median follow up time abemaciclib + endocrine therapy (ET) resulted
in a 29% reduction in the risk of developing an invasive disease-free survival
(IDFS) event [hazard ratio (HR) = 0.71, 95% confidence interval (CI)
0.58-0.87; nominal P = 0.0009]. At the additional follow-up analysis, with 27
months median follow-up and 90% of patients off treatment, IDFS (HR = 0.70,
95% CI 0.59-0.82; nominal P < 0.0001) and DRFS (HR = 0.69, 95% CI 0.57-0.83;
nominal P < 0.0001) benefit was maintained. The absolute improvements in
3-year IDFS and distant relapse free survival (DRFS) rates were 5.4% and 4.2%,
respectively. Whereas a high centrally determined Ki-67 index defined as
greater than or equal to 20% was prognostic for recurrence in this treatment
setting, it was not predictive of the treatment effect as abemaciclib benefit
was observed regardless of Ki-67 index. Safety data were consistent with the
known abemaciclib risk profile.7 This is supported by updates to the NCCN
Guidelines and International Ki67 workgroup.6,8

The clinical utility of testing for hormone receptors in in-situ breast cancer
differs from those of invasive disease. 2020 ASCO/CAP Guidelines for Ductal
Carcinoma in-situ (DCIS) testing state: "ER testing in cases of newly
diagnosed DCIS (without associated invasion) is recommended to determine
potential benefit of endocrine therapies to reduce risk of future breast
cancer. PR testing is considered optional" [recommendation 4, and subsequent
discussion].5 This is supported by the peer reviewed literature which supports
the use of ER testing for in-situ breast neoplasia. The addition of PR testing
should be determined in those settings where it has been deemed reasonable and
necessary and its relevance has been documented in the pathology report and
individual patient. Clinical guidelines have not been established for the use
of Her2 or other biomarkers in patients with non-invasive breast neoplasia.5  
  
Basal phenotype markers (eg, IHC for CK5) are not routinely necessary. IHC
stains such as E-cadherin, p27, or high molecular weight cytokeratin to
distinguish ductal from lobular differentiation are not reasonable and
necessary on every breast case, nor are myoepithelial cell markers such as p63
or smooth muscle myosin heavy chain routinely necessary on every case. The use
of these markers should be determined by the pathologist when there are
ambiguous histologic/morphologic findings on H&E and the distinction between
lobular and ductal differentiation or usual ductal hyperplasia (UDH) versus
atypical ductal hyperplasia (ADH) and DCIS are critical to the clinical
management of the patient and its rationale is documented in the pathology
report.9  
  
 **Special Stains and/or IHC for Gastrointestinal (GI) Pathology**  
Pathologists are often called upon to microscopically diagnose abnormalities
seen on endoscopic exam of the esophagus, stomach, duodenum and colon. Biopsy
specimens constitute an important diagnostic patient service. Most normal and
abnormal conditions of these organs can be detected by the use of the routine
H&E stain alone.  
  
For most esophageal, gastric and duodenal specimens, it is not reasonable or
necessary to perform special stains such as alcian blue - periodic acid Schiff
(AB-PAS), or other mucin stains, such as diastase - PAS (D-PAS), or IHC stains
such CDX-2 to determine if clinically meaningful intestinal metaplasia is
present. In addition, it is not usually reasonable and necessary to perform
special stains or IHC to determine the presence of H. pylori organisms.10-12

Scientific data demonstrates that the combined number of gastric biopsies
requiring special stains or IHC is roughly 20% of biopsies received and
examined in a pathology practice. GI specialty practices with a large GI
referral base or GI consultant pathologists may sometimes exceed this relative
number of special stains/IHC, but one would not expect to see routine high
utilization of special stains or IHC. To check utilization, we encourage
providers to perform a self-audit on the number of separate gastric biopsies
as compared to ancillary stains. The ancillary stain group should be less than
20% of the total gastric biopsies submitted. Providers that exceed the 20%
criteria may be subject to additional action.13,14

Over-utilization of special stains has also been observed with duodenal
biopsies where CD3 and AB/D-PAS are reportedly used to help exclude
intraepithelial lymphocytosis and gastric metaplasia. Both of these
conditions, if present, are easily recognizable on H&E morphology. Mucin
stains such as AB-PAS or DPAS would be reasonable and necessary in limited
circumstances, and rarely is CD3 warranted on duodenal biopsies which show
villous architectural abnormalities.  
  
Architectural and histologic features define colonic polyps including
hyperplastic, inflammatory, and adenomatous lesions. Special stains and/or IHC
stains are not reasonable and necessary for colon polyps despite textbooks
noting, for example, thickened subepithelial collagen demonstrated by
trichrome or collagen staining in hyperplastic polyps, or carcinoembryonic
antigen (CEA) overexpression in hyperplastic polyps. While the information is
of academic interest, special stains are not reasonable and necessary to make
the diagnosis of various colonic polyps.

Lynch Syndrome (LS) is a genetic predisposition to colorectal cancer (CRC) and
certain other malignancies, as a result of an autosomal dominant germline MMR
gene mutation. There is benefit in identifying an asymptomatic individual with
LS as it allows for early and intensive surveillance to detect colon polyps,
which can prevent malignancies and reduce the risk of premature death.15

  * LS tumor screening for microsatellite instability (MSI)/deoxyribonucleic acid (DNA) mismatch repair (MLH1, MSH2, MSH6 and PMS2) by qualitative IHC is considered medically necessary and covered by Medicare for individuals with newly diagnosed colorectal cancer or endometrial cancer.

No definitive or clearly superior algorithm for LS screening has been
recommended. MSI testing or IHC testing (with or without _BRAF V600E_ mutation
testing) for MLH1, MSH2, MSH6 and PMS2 of the tumor tissue are examples of
preliminary testing strategies that could be used to select patients for
subsequent diagnostic testing. Diagnostic testing involves MMR gene mutation
(and deletion/duplication) testing of the proband, usually using a blood
sample. LS is most commonly caused by mutations in the 2 MMR genes, MLH1 and
MSH2 and less commonly by mutations in MSH6 and PMS. The presence of a BRAF
mutation essentially excludes LS as virtually 100% of individuals with LS do
not carry the BRAF mutation. The use of BRAF mutation testing by IHC is
usually restricted to CRC cases with absent staining for MLH1.16

If IHC is normal and there is clinical evidence to consider additional
testing, MMR gene mutation testing may be warranted. IHC testing for LS is
qualitative and does not require the use of tumor morphometry for evaluation.  
  
 **Special Stains and/or IHC for Prostate Pathology**  
The accuracy of the pathologic diagnosis of prostate cancer is critical for
optimal patient care. The diagnosis can usually be made on morphologic
features such as growth pattern, nuclear atypia and the absence of basal
cells. However, it may be difficult to reach a firm diagnosis by routine H&E
stain for small foci of cancer in needle biopsies because many benign
conditions can mimic prostate cancer.17  
  
The IHC diagnosis of prostate cancer largely depends on panels of markers
because no absolutely specific and sensitive marker for prostate cancer has
yet been identified. These panels usually include at least 1 basal cell
marker, such as high-molecular-weight cytokeratin (HMWCK) or p63, and the
prostate cancer-specific marker, alpha-methyl-CoA-Racemase (AMACR). Although
AMACR is considered a useful IHC marker for prostate cancer, because of non-
standardized immunostaining protocols, interpretation criteria and
heterogeneous staining pattern, there is wide variation in the sensitivity and
specificity of AMACR immunoreactivity in prostate biopsies. Furthermore,
because AMACR expression has been demonstrated in high-grade prostatic
intraepithelial neoplasia (PIN), atypical adenomatous hyperplasia/adenosis and
nephrogenic adenoma, it is recommended that AMACR is best restricted to the
evaluation of morphologically highly suspicious foci in which negative
immunoreactivity of basal cell markers alone is insufficient to establish a
diagnosis of cancer.18,19  
  
PTEN and MYC may provide some prognostic information but neither is part of
any standard treatment protocol and neither should be routinely performed.20
ERG is another IHC that is more likely to be positive in cancer than in benign
tissue, but it does not add information to conventional PIN4 testing.21
Similarly, neuroendocrine markers, such as IHC for synaptophysin, may be
indicated in cases of recurrent/metastatic prostate carcinoma that have
undergone small cell transformation after hormone therapy. The latter marker
is only necessary for high grade, undifferentiated tumors and should not be
used routinely.17  
  
PIN4 is an IHC cocktail of CK5/14, p63 and P504S that is used primarily to
differentiate normal and neoplastic epithelial tissues. In prostate tissue,
CK5 and CK14 are detected in basal cells of normal glands and PIN which is a
precursor lesion to prostatic adenocarcinoma. However, expression of CK5 and
CK14 is not identified in invasive prostatic adenocarcinoma. P63 is detected
in nuclei of basal epithelium in normal prostate glands, but is not expressed
in malignant prostate tumors. The use of PIN4 is best restricted to evaluation
of morphologically highly suspicious foci because P504S (aka AMACR) is not
specific for prostatic adenocarcinoma.

The International Society of Urological Pathology (ISUP) recommendations state
that at the current time, there are no prognostic IHC or molecular studies
that are recommended to be routinely performed on biopsy or resection
specimens.22  
  
 **Special Stains and/or IHC for Lung Cancer**

Experts in pulmonary pathology recommend starting the evaluation of non-small
cell carcinomas with a combination of TTF-1 and p40 or p63 IHCs. Often these
two stains are all that are needed to come to a reasonable diagnosis and
retain enough tumor sample to complete molecular studies. In rare patients, a
few additional IHCs or mucin stains may be needed.  
  
 **Ki-67/MIB-1**  
Ki-67 and MIB-1 monoclonal antibodies are directed against different epitopes
of the same proliferation-related antigen. These stains are used to determine
the proliferative rate of a tumor. Ki-67 antigen or protein (hereafter Ki-67)
is present during all active phases of the cell cycle (G1, S, G2, and
mitosis), but is absent from resting cells (G0). By measuring the amount of
tumor cells expressing Ki-67, an estimate of DNA synthesis can be determined
which has been found comparable to a mitotic count performed on a standard H&E
slide. Furthermore, Ki-67/MIB-1 antibodies have suffered from a lack of
international standardization which has limited their clinical
usefulness.23,24 This is noted above in the discussion of breast cancers.

Ki67 has been shown to be useful in the management and grading of
neuroendocrine tumors of the gastrointestinal tract and pancreas. The North
American Neuroendocrine Tumor Society (NANETS) in its consensus 2020
guidelines for the management and treatment of neuroendocrine tumors states
these tumors should be graded according to the World Health Organization (WHO)
Classification of Digestive system Tumors. Grading recommends "Ki67 and/or
mitotic rate should be obtained. When both mitotic rate and Ki67 are obtained
and grade is discrepant the higher grade determined by mitotic rate or Ki67 is
assigned with Grade 1 (G1) tumors showing <2 mitoses/10 HPF or <3% Ki67, Grade
2 (G2) tumors showing 2-20 mitoses/10 HPF or 3-20% Ki67 and Grade 3 (G3)
tumors showing >20 mitoses/10 HPF or Ki67 > 20%".25

When referring to Thoracic (lung) neuroendocrine tumors the NANETS society in
the same consensus 2020 guidelines quoted above states "mitotic rate should be
obtained. Use of the WHO and International Association for the Study of Lung
Cancer grading system is recommended. Mitotic rate in mitoses /10 HPF is
recommended. Ki-67 may be considered. Ki-67 (when necessary) is recommended
along with mitotic rate to classify Grade 3 (G3) neuroendocrine lung tumors
where mitotic rate >10 mitoses/10 HPF and Ki67 >20% classifies these as poorly
differentiated neuroendocrine tumors".

Ki67 can be used as an aid in the distinction of low grade versus high grade
neuroendocrine tumors where the biopsy or cytology specimen is limited or
suffers from significant artefact.25

Ki-67 by IHC has clinical utility in the workup of lymphomas. Ki-67 has
several established applications including:

  * Final confirmation for the diagnosis of any low-grade lymphoma. A number of publications show a worse prognosis for follicular lymphomas which appear to be grade 1 or 2 but demonstrate high Ki-67 labeling. Similarly, small lymphocytic lymphomas/CLL with a high proliferative rate ("prolymphocytic progression") may be best detected with Ki-67.
  * Distinguishing higher versus lower grade mantle cell lymphoma. A small percentage of cases behave as low grade rather than intermediate grade, and Ki-67 is the most accurate means to detect this subgroup. In addition, distinguishing the highly aggressive blastoid variant is aided by Ki-67 IHC testing.
  * Recognizing Burkitt and Burkitt-like grouping as distinct from diffuse large B-cell type. One of the most important qualifying criteria is Ki-67 labeling at greater than 90%.
  * Plasma cell myeloma proliferative rate has long been established as 1 of the most accurate prognostic markers.

**IHC for Predictive Marker Tumor Profiling**  
ER, PR, and Her2 hormonal receptor status have demonstrated clinical utility
in invasive breast cancer, as well as ER, and PR when appropriate, for in-situ
breast cancer. ER and PR are performed by IHC specifically for tamoxifen
therapy. Her2 testing has proven clinical utility in esophago-gastric and
gastric cancers to determine response to trastuzumab.  
  
Similarly, the efficacy of imatinib, a CD117 inhibitor, is determined by the
mutation status of CD117 expression (c-KIT mutation). CD117 by IHC has a
proven clinical benefit in GIST, some advanced dermatofibrosarcoma protuberans
(DFSP), some lymphoblastic and myeloid leukemias, and mast cell tumors, and is
a covered Medicare service when medically necessary. All predictive tumor
profiles must have peer reviewed analytical and clinical validity.  
  
However, IHC testing as above is distinctly different from chemotherapy
sensitivity and/or resistance testing profiles offered by some labs to assist
physicians in their selection of specific chemotherapeutic agents based on IHC
antigen or protein expression in individual tumors. The goal stated by these
profiles is to select a drug or combination of drugs from a panel of drugs to
which a tumor has greater expression, and to avoid drugs to which the tumor
has less expression.  
  
Neither the ASCO nor the NCCN has endorsed chemosensitivity tumor profile
testing by IHC. ASCO has stated, "the use of CSRA's (chemosensitivity and
resistance assays) to select chemotherapeutic agents for individual patients
is not recommended outside of the clinical trial setting." While the NCCN's
Guidelines for Ovarian Cancer (V3.2014) states "chemosensitivity/resistance
and/or other biomarker assays are being used in some NCCN member institutions
for decisions related to future chemotherapy in situations where there are
multiple equivalent chemotherapy options available.26 The current level of
evidence is not sufficient (Category 3) to supplant standard of care
chemotherapy." The NCCN panel also stated that in vitro chemosensitivity
testing to choose a chemotherapy regimen for recurrent disease should not be
recommended due to lack of demonstrated efficacy.

Chemosensitivity profile tumor panels, regardless of whether it is performed
by IHC or chromogenic in-situ hybridization (CISH), is not reasonable and
necessary for the reasons cited above.  
  
Note, some of these markers are legitimate biomarkers for specified drugs when
performed by mutation analysis or FISH testing.  
  
**IHC for Cervical/Gyn/Bladder/Kidney Tumors**  
Claims data indicate combinations of gram stain, PAS, Ki-67, p16 and ProExC
stains on all cervical biopsies from select pathology practices, and
combinations of p53, Ki-67, CD20 and CD44 on bladder biopsies from select
pathology practices.26  
  
The use of IHC stains in endometrial cancer, ovarian cancer or a kidney
neoplasm requires adequate documentation in the pathology report, such as
"Because the differential histologic diagnosis is between an endometrioid
carcinoma and a serous carcinoma, I performed an xxx stain. The controls
worked appropriately and the results were positive indicating the tumor is a
yyy."  
  
 **IHC for Skin & Cutaneous/Soft Tissue/ Central Nervous System (CNS) &
Peripheral Nervous System (PNS) Lesions**  
It is well recognized that most skin lesions are diagnosed with routine H&E
slides. That is the case for most melanomas and other pigmented lesions as
well.  
  
Soft tissue masses may require stains (e.g., smooth muscle differentiation in
a malignant mass) but most do not.  
  
The primary role of IHC for CNS and PNS lesions is to differentiate primary
from metastatic lesions.

New evidence and guidelines have resulted in changes made to the policy to
ensure coverage for special stains that now meet requirements of reasonable
and necessary. The areas where changes are supported by evidence have been
made throughout the policy with supporting literature references.