Tumor-size responses to first-line is a predictor of overall survival in metastatic colorectal cancer.

Early tumor shrinkage (ETS) has been reported to be associated with survival of metastatic colorectal cancer (mCRC) patients. Our aim was to analyze long-term tumor-size evolution, according to early mCRC best responses during the first-line therapy, to evaluate first best response-survival links. Sixty-five patients with unresectable mCRCs, treated between 2010 and 2015, were included retrospectively in this descriptive monocenter study and grouped according to their RECIST 1.1 first-line best responses: progressive disease (PD Tumor loads of ETS Tumors responding to first-line chemotherapy also responded better to subsequent lines, whereas PD • Early shrinking tumors under first-line chemotherapy responded better to subsequent lines, maintaining low tumor loads, potentially explaining the link between early tumor shrinkage and overall survival of metastatic colorectal cancer (mCRC) patients. • mCRCs progressing under first-line chemotherapy remained refractory to other therapies and their tumor loads increased rapidly. • Even outside a clinical trial, an early first CT scan reevaluation with RECIST criteria 8 weeks after starting first-line therapy is crucial to determine long-term mCRC evolution.