Characterizing the Tumor Microenvironment of Colorectal Cancer Patients

Genetic and cellular screening is essential for characterizing specific cell genotypes and phenotypes when treating diseases, providing fundamental information on treatment prognosis. Thanks to immunohistochemistry in combination with tissue cytometry and genetic sequencing advancements, characterization of the tumor microenvironment reveals the underlying mechanisms of immunotherapy in oncology and facilitates the discovery of critical predictive biomarkers, fostering more beneficial therapy and better survival rates. 

Metastatic Colorectal Cancer 

Colorectal cancer (CRC) remains one of the top three most common cancer types in men and women worldwide.1 Globally, it is the fifth cause of death relating to cancer in women and the fourth cause in men.

Despite current therapeutic advancements, it is predicted that by 2030, the harmful impact of CRC on global health will increase by 60%.2

Almost half of CRC patients are also diagnosed with metastasis during disease progression and although clinical outcomes are improving, metastatic (m)CRC patients only have a median overall survival of up to 30 months.3  


Like most cancers, mCRC treatment has been chemotherapy with biological agents. However, immunotherapy treatments are now beginning to show clinical benefits to mCRC patients.

Immune checkpoint inhibitors (ICIs) are a well-realized immunotherapy technique for several types of solid tumors, and in recent years, they have started being utilized to treat mCRC patients.4  

High microsatellite instability (MSI-H) and mismatch repair protein deletion (dMMR) has become a vital biomarker for stratifying patients with advanced mCRC in treatment groups.

ICIs targeting the anti-PD-1/PD-L1 pathway have high clinical efficacy in patients with MSI-H/dMMR. However, only 5% of patients with advanced mCRC exhibit MSI-H/dMMR, and other patients generally have microsatellite stability (MSS)/proficient mismatch repair proteins (pMMR).5 

Patients with MSS/pMMR do not display a positive response to single ICIs, and various immune combination therapy treatments have shown little benefit to patients exhibiting MSS/pMMR.

In current trials, only 1.9% of patients with liver metastases display an overall objective remission rate. On top of this, there are no conventional biomarkers for MSS-type CRC.5 

The Need for Screening and Biomarkers 

Tumors of MSS-type patients are classified as ‘immune cold tumors’ because immune desert types with low levels of tumor lymphocyte infiltration and tumor mutational load mainly characterize the immune microenvironment.

A combination of therapies and screening strategies are used to alter and monitor the immune microenvironment to increase the efficacy of current immunotherapies. Such treatments transform “immune cold tumor” microenvironments into “immune hot tumors” and aid the discovery of biomarkers.5  

Tumor mutational burden (TMB) status was found to be related to immunotherapy benefits in patients. However, the clinical significance of TMB is still under debate.

Tumor-infiltrating lymphocytes (TILs) are also closely linked to treatment prognosis in mCRC, but the identification of more accurate biomarkers is drastically needed to guide the screening of patients with MSS mCRC.

Exploration of the tumor microenvironment is required to decipher which MSS-type CRC patients can clinically benefit from immunotherapy.5 

Case Study: 50-Year-Old Patient with mCRC/Liver Metastasis Recovers with Immunotherapy 

A 50-year-old patient with MSS-type CRC and PD-L1-negative recurrent hepatopulmonary metastases underwent complete remission and prolonged benefits from immunotherapy treatments after systematic treatments had previously failed.  

The case study evaluated the characteristics of the tumor microenvironment during treatment to gain insight into the mechanisms of immunotherapy benefits. This enabled them to identify which phenotypes imply a favorable response and discover potential prognostic biomarkers.

Genetic and multiple immunohistochemical tests revealed that mutations in the DNA damage repair pathway genes and TILs likely contributed to the clinical benefits encountered. 

The tissue cytometry platform TissueFAXS SL including the image analysis solution StrataQuest was used to determine the cellular phenotypes linked to successful clinical benefits. TissueFAXS SL was used to acquire whole slide images of the stained tissue sections, while StrataQuest was used to perform image analysis to quantify specific cellular phenotypes based on various immune cell markers. This revealed that the tumor microenvironment was enriched in immune cells, specifically CD8+ T cells, CD68+ macrophages, and CD163+ macrophages. 

TILs are vital constituents of the tumor microenvironment and can impact tumor growth, metastasis, and immunotherapy effectiveness.

In other studies, some TILs, particularly PD-1 expressing CD8+ T cells, were associated with a better survival rate in CRC.

Tumor-associated macrophages were also highly abundant in the tumor microenvironment and related to better therapeutic outcomes. This supports evidence that suggests TILs are essential bioindicators of the effectiveness of immunotherapy in MSS mCRC patients.

DNA damage repair gene mutations in advance mCRC might also be an essential biomarker in screening for ICIs’ clinical benefits in MSS mCRC patients. This will hopefully increase the number of MSS mCRC patients that can benefit from immunotherapy.  


This case study shows how immunotherapy can provide significant clinical benefits, even compared to more traditional chemotherapies, in patients with advanced MSS mCRC.

This study demonstrates the necessity of identifying new, effective predictive biomarkers to guide the screening for immunotherapy benefits in MSS mCRC patients. With TissueFAXS and StrataQuest, researchers can uncover cell phenotypes, immune mechanisms, and biomarkers within the tumor microenvironment to provide more effective immunotherapies. 


References and Further Reading

  1. Ferlay, J., Colombet, M., Soerjomataram, I., Mathers, C., Parkin, D.M., Piñeros, M., Znaor, A. and Bray, F. 2019. Estimating the global cancer incidence and mortality in 2018: GLOBOCAN sources and methods. International journal of cancer. 144(8), pp.1941-1953.
  2. Arnold, M., Sierra, M.S., Laversanne, M., Soerjomataram, I., Jemal, A. and Bray, F., 2017. Global patterns and trends in colorectal cancer incidence and mortality. Gut. 66(4), pp.683-691.
  3. Oliveira, A.F., Bretes, L. and Furtado, I., 2019. Review of PD-1/PD-L1 inhibitors in metastatic dMMR/MSI-H colorectal cancer. Frontiers in oncology. 9, p.396.
  4. Huyghe, N., Baldin, P. and Van den Eynde, M. 2020. Immunotherapy with immune checkpoint inhibitors in colorectal cancer: what is the future beyond deficient mismatch-repair tumours? Gastroenterology report. 8(1), pp.11-24.
  5. Song, Y., Long, J., Su, X., Chen, Z., He, Y., Shao, W., Wang, B. and Chen, C. 2023. Case report: genetic and immune microenvironmental characteristics of a rectal cancer patient with MSS/PD-L1-negative recurrent hepatopulmonary metastasis who achieved complete remission after treatment with PD-1 inhibitor. Frontiers in Immunology. 14, p.1197543.

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