[What is the contribution of tumor response in colorectal cancer?]

Tumor size reduction after cancer treatment is evaluated by tumor response. It is often the primary objective of phase II clinical trials. The WHO and RECIST criteria are now internationally recognized for the quantification of tumor response in clinical trials. This literature review article focuses on the interest of measuring tumor response according to these criteria in terms of clinical benefit for patients with metastatic colorectal cancer (mCRC): metastasis resection, survival and improving quality of life. In patients with mCRC and initially resectable metastases, tumor response following preoperative chemotherapy is an independent prognosis factor for survival and a way of testing tumor sensitivity to the chemotherapy regime; it allows and/or facilitates metastases resection. In patients with mCRC and potentially resectable metastases, obtaining an objective tumor response to allow secondary metastasis resection is one of the primary objectives of chemotherapy. In patients with mCRC and non-resectable metastases, tumor response may provide individual benefit in terms of control of symptoms and quality of life and may favor a survival benefit. Despite the limitations of the RECIST criteria, no other morphological or functional radiological criterion has to date achieved consensus up in terms of availability, reproducibility, sensitivity, specificity, clinical relevance and cost. Finally, although there is no high-level of evidence, tumor response has prognostic value for metastases resection in mCRC and is a therapeutic objective in patients with potentially resectable metastases or symptomatic advanced disease.