A biomarker may help identify which colorectal cancer patients could benefit from immunotherapy

For only a small proportion of people with colorectal cancer, immunotherapy is currently an option. In colon cancer, that figure is around 5%, and even then, the treatment does not work in every case. Now, researchers led by the Hospital del Mar Research Institute and IRB Barcelona have identified a biomarker that could help clinicians better predict which patients are more likely to respond, while also offering new information about prognosis. The study has been published in Gut.

The marker is called CTHRC1, and it is not found in the tumour cells themselves, but in cells around the tumour known as cancer-associated fibroblasts. These cells are part of the tumour microenvironment: the surrounding tissue that helps shape how a cancer grows, interacts with the immune system and responds to treatment. According to the study, the presence of these CTHRC1-positive fibroblasts is associated with lower immunogenicity, poorer outcomes and more limited benefit from immunotherapy.

One of the most relevant aspects of the work is its potential usefulness in real clinical settings. The researchers show that this biomarker can be detected by immunohistochemistry, a standard technique routinely used in pathology departments. To validate the finding, the team analysed 17 cohorts, including samples from nearly 3,000 patients, and confirmed the results in samples from several national and international hospitals, including Hospital del Mar.

Beyond helping to identify who may benefit from immunotherapy, the biomarker could also improve prognosis. The study links high CTHRC1 levels to TGF-beta activity in the tumour microenvironment, a pathway associated with worse disease outcomes and treatment resistance. In that sense, the work not only points to a new clinical marker but also to a biological mechanism that may eventually be targeted therapeutically.

Overall, the findings reinforce an idea that has become increasingly important in cancer research: to understand how a tumour will behave, it is not enough to look only at the tumour itself. The surrounding cells also matter. In colorectal cancer, that broader view may now help refine treatment decisions using tools that hospitals already have at hand.