Is the tumour microenvironment a critical prognostic factor in early-stage colorectal cancer?
Authors: G. Nyamundanda, E. Fontana, A. Sadanandam
Journal: Annals of Oncology (2019)

The TNM staging system remains the cornerstone of risk assessment in patients with early-stage colorectal cancer (CRC). However, clinical behaviour is diverse within the same stages, making prognostication an imprecise science. Microsatellite instability (MSI) is the only biomarker routinely considered beyond TNM, although a range of major genomic changes is well established, with contradictory evidence in outcome prediction [1.Dienstmann R. Mason M.J. Sinicrope F.A. et al.Prediction of overall survival in stage II and III colon cancer beyond TNM system: a retrospective, pooled biomarker study.Ann Oncol. 2017; 28: 1023-1031Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar, 2.Labianca R. Nordlinger B. Beretta G.D. et al.Early colon cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.Ann Oncol. 2013; 24: vi64-72Abstract Full Text Full Text PDF PubMed Scopus (551) Google Scholar]. So what other markers could improve prognostic precision? CRC heterogeneity has now been comprehensively characterised at the transcriptomic level as between three and six prognostic and potentially predictive subtypes [3.Sadanandam A. Lyssiotis C.A. Homicsko K. et al.A colorectal cancer classification system that associates cellular phenotype and responses to therapy.Nat Med. 2013; 19: 619-625Crossref PubMed Scopus (586) Google Scholar, 4.De Sousa E Melo F. Wang X. Jansen M. et al.Poor-prognosis colon cancer is defined by a molecularly distinct subtype and develops from serrated precursor lesions.Nat Med. 2013; 19: 614-618Crossref PubMed Scopus (485) Google Scholar, 5.Marisa L. de Reyniès A. Duval A. et al.Gene expression classification of colon cancer into molecular subtypes: characterization, validation, and prognostic value.PLoS Med. 2013; 10: e1001453Crossref PubMed Scopus (692) Google Scholar, 6.Roepman P. Schlicker A. 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The CMS classification has shown prognostic significance in both the early and advanced settings in multiple cohorts from high-quality clinical trials testing contemporary regimens [10.Fontana E. Eason K. Homicsko K. Sadanandam A. Molecular classification of colon cancer: perspectives for personalized adjuvant therapy.Curr Colorectal Cancer Rep. 2016; 12: 296-302Crossref Scopus (1) Google Scholar, 11.Lenz H.J. Ou F.S. Venook A.P. et al.Impact of consensus molecular subtype on survival in patients with metastatic colorectal cancer: results from CALGB/SWOG 80405 (Alliance).J Clin Oncol. 2019; 37: 1876-1885Crossref PubMed Scopus (67) Google Scholar, 12.Song N. Pogue-Geile K.L. Gavin P.G. et al.Clinical outcome from oxaliplatin treatment in stage II/III colon cancer according to intrinsic subtypes: secondary analysis of NSABP C-07/NRG oncology randomized clinical trial.JAMA Oncol. 2016; 2: 1162-1169Crossref PubMed Scopus (84) Google Scholar, 13.Fontana E. Eason K. Cervantes A. et al.Context matters-consensus molecular subtypes of colorectal cancer as biomarkers for clinical trials.Ann Oncol. 2019; 30: 520-527Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar]. While CMS2 and CMS3 primarily represent epithelial cancer cell heterogeneity, CMS1 and CMS4 also include cellular components of the tumour microenvironment, mainly immune cells and stromal fibroblasts [9.Guinney J. Dienstmann R. Wang X. et al.The consensus molecular subtypes of colorectal cancer.Nat Med. 2015; 21: 1350-1356Crossref PubMed Scopus (1863) Google Scholar, 10.Fontana E. Eason K. Homicsko K. Sadanandam A. Molecular classification of colon cancer: perspectives for personalized adjuvant therapy.Curr Colorectal Cancer Rep. 2016; 12: 296-302Crossref Scopus (1) Google Scholar, 14.Dienstmann R. Vermeulen L. Guinney J. et al.Consensus molecular subtypes and the evolution of precision medicine in colorectal cancer.Nat Rev Cancer. 2017; 17: 79-92Crossref PubMed Scopus (332) Google Scholar]. The immune microenvironment is known to contribute to CRC patient prognosis [15.Mlecnik B. Tosolini M. Kirilovsky A. et al.Histopathologic-based prognostic factors of colorectal cancers are associated with the state of the local immune reaction.J Clin Oncol. 2011; 29: 610-618Crossref PubMed Scopus (630) Google Scholar]. Among tumour microenvironment cells, immune cell infiltrates, specifically cytotoxic T lymphocytes (CytoLym, enriched in CMS1), are associated with better outcomes in early-stage CRC patients [15.Mlecnik B. Tosolini M. Kirilovsky A. et al.Histopathologic-based prognostic factors of colorectal cancers are associated with the state of the local immune reaction.J Clin Oncol. 2011; 29: 610-618Crossref PubMed Scopus (630) Google Scholar]. The CMS4 subtype is enriched for cancer-associated fibroblasts (CAFs) and has a poor prognosis [9.Guinney J. Dienstmann R. Wang X. et al.The consensus molecular subtypes of colorectal cancer.Nat Med. 2015; 21: 1350-1356Crossref PubMed Scopus (1863) Google Scholar, 16.Calon A. Lonardo E. Berenguer-Llergo A. et al.Stromal gene expression defines poor-prognosis subtypes in colorectal cancer.Nat Genet. 2015; 47: 320-329Crossref PubMed Scopus (552) Google Scholar]. Is it possible that subtype-specific prognosis is driven by the microenvironment? To address this question and following up on their previous study [1.Dienstmann R. Mason M.J. Sinicrope F.A. et al.Prediction of overall survival in stage II and III colon cancer beyond TNM system: a retrospective, pooled biomarker study.Ann Oncol. 2017; 28: 1023-1031Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar], Dienstmann et al. explored whether tumour microenvironment features such as CytoLym and CAFs are stronger determinants of disease-free survival (DFS) in early-stage CRC patients than the known genomic aberrations (MSI, BRAF and KRAS mutational status) and CMS subtypes [17.Dienstmann R. Villacampa G. Sveen A. et al.Relative contribution of clinicopathological variables, genomic markers, transcriptomic subtyping and microenvironment features for outcome prediction in stage II/III colorectal cancer.Ann Oncol. 2019; 30: 1622-1629Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar]. Their large, retrospective study of several public and private clinically annotated stage II/III CRCs (n = 2, 636), both untreated (n = 1, 656) and treated (n = 980), evaluated CMS1/4 subtype scores and microenvironment-based (CytoLym and CAF) continuous scores in silico. In a multivariable model, clinicopathological (including TNM) and microenvironment features were independent prognostic factors. Clinicopathological variables explained the majority (56%–77%) of variation in DFS, followed by immune stromal infiltrating markers (14%–35%), while only <6% of DFS variation was explained by CMS and genomic factors. Moreover, CAF scores were associated with poor prognosis exclusively in stage III cancers while CytoLym scores were associated with good prognosis specifically in stage II and microsatellite stable cancers. Hence, CMS4 and MSI subtypes (enriched for CAFs and CytoLym, respectively [14.Dienstmann R. Vermeulen L. Guinney J. et al.Consensus molecular subtypes and the evolution of precision medicine in colorectal cancer.Nat Rev Cancer. 2017; 17: 79-92Crossref PubMed Scopus (332) Google Scholar, 16.Calon A. Lonardo E. Berenguer-Llergo A. et al.Stromal gene expression defines poor-prognosis subtypes in colorectal cancer.Nat Genet. 2015; 47: 320-329Crossref PubMed Scopus (552) Google Scholar]) were not prognostic when these specific microenvironment features were included [17.Dienstmann R. Villacampa G. Sveen A. et al.Relative contribution of clinicopathological variables, genomic markers, transcriptomic subtyping and microenvironment features for outcome prediction in stage II/III colorectal cancer.Ann Oncol. 2019; 30: 1622-1629Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar]. This study adds to the evidence that the tumour microenvironment plays a crucial prognostic role in CRC. The authors must be appreciated for their efforts in collecting over 2600 patient samples from public and private (including clinical trial) datasets. Their findings are consistent with previous studies, in particular with the immunohistochemistry assay Immunoscore®, which has been extensively validated in early-stage CRCs [18.Pages F. Mlecnik B. Marliot F. et al.International validation of the consensus Immunoscore for the classification of colon cancer: a prognostic and accuracy study.Lancet. 2018; 391: 2128-2139Abstract Full Text Full Text PDF PubMed Scopus (685) Google Scholar]. Overall, this represents an excellent summary of the relative contribution of clinicopathological and molecular features in explaining DFS. Validation of these current results in additional, high-quality datasets is recommended, including those in oxaliplatin-treated stage III cancers. However, the study has limitations. Genomic data (MSI and BRAF mutation) were missing for a large number of samples, which were instead imputed computationally, although the prevalence of these aberrations was similar to those previously reported [2.Labianca R. Nordlinger B. Beretta G.D. et al.Early colon cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.Ann Oncol. 2013; 24: vi64-72Abstract Full Text Full Text PDF PubMed Scopus (551) Google Scholar]. Conversely, all included samples had CytoLym and CAF scores available. This inconsistent availability of data may have biased the statistical analyses. Hence, the results of these exploratory analyses in this study of multiple retrospective cohorts need to be interpreted appropriately. Age is usually considered a clinical factor when balancing chemotherapy benefit against side-effects [2.Labianca R. Nordlinger B. Beretta G.D. et al.Early colon cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.Ann Oncol. 2013; 24: vi64-72Abstract Full Text Full Text PDF PubMed Scopus (551) Google Scholar]. As highlighted by the authors [17.Dienstmann R. Villacampa G. Sveen A. et al.Relative contribution of clinicopathological variables, genomic markers, transcriptomic subtyping and microenvironment features for outcome prediction in stage II/III colorectal cancer.Ann Oncol. 2019; 30: 1622-1629Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar], age accounted for a significant proportion of DFS, especially in the untreated (and older) population, who more often experience non-cancer-related deaths. Hence, it is worth considering only CRC-related relapses for DFS. Sidedness is a known surrogate biomarker of complex CRC biology: while the poor prognosis and reduced response to anti-epidermal growth factor receptor therapy in the right-sided metastatic setting is increasingly recognised, the prognostic role of sidedness in early-stage CRC is less clear [19.Petrelli F. Tomasello G. Borgonovo K. et al.Prognostic survival associated with left-sided vs right-sided colon cancer: a systematic review and meta-analysis.JAMA Oncol. 2017; 3: 211-219Crossref PubMed Scopus (287) Google Scholar]. The current study shows that right-sided early-stage (II and III) CRCs have a better DFS than left-sided CRCs irrespective of MSI status (using partially imputed data) [17.Dienstmann R. Villacampa G. Sveen A. et al.Relative contribution of clinicopathological variables, genomic markers, transcriptomic subtyping and microenvironment features for outcome prediction in stage II/III colorectal cancer.Ann Oncol. 2019; 30: 1622-1629Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar], similar to previously published results [20.Kennecke H.F. Yin Y. Davies J.M. et al.Prognostic effect of sidedness in early stage versus advanced colon cancer.Health Sci Rep. 2018; 1: e54Crossref PubMed Scopus (6) Google Scholar]. Nevertheless, this observation requires further validation using well-annotated data to assess whether these observations are generalisable to early CRCs in the real clinical setting. The MicroCells approach was limited to detecting only a few immune cell types and did not include, for example, T regulatory cells and specific macrophage subsets, which may be important in governing pro- and anti-inflammatory responses in tumours and, therefore, prognosis. Furthermore, the scores for the microenvironment cell types may vary depending on the cell-type markers and computational methods used. It is worth remembering that computational methods require rigorous validation using established immunohistochemistry or similar experimental methods before clinical application. Nevertheless, the association between CytoLym and MSI status suggests that this study included the most relevant microenvironment scores and important immune populations. This interesting study now prompts the question of what other factors beyond the microenvironment may affect prognosis in patients with early-stage CRCs. Epigenetics, colonic crypt cell types (similar to previously reported [3.Sadanandam A. Lyssiotis C.A. Homicsko K. et al.A colorectal cancer classification system that associates cellular phenotype and responses to therapy.Nat Med. 2013; 19: 619-625Crossref PubMed Scopus (586) Google Scholar]), tumour mutational burden, and neoantigens are promising candidates. Whatever the answer, robust and clinically relevant biomarkers and assays are mandatory for effective clinical translation, which may need to be developed in the future based on the current study. Nevertheless, with further validation, these findings will hopefully facilitate our understanding of the relative contributions of cancer cells and the microenvironment in determining prognosis in early-stage CRC patients and refine personalised medicine approaches in the future. None declared.