Abstract
Achieving tumor shrinkage may be a clinically relevant improvement in the treatment of metastatic colorectal cancer (mCRC). The present study attempted to evaluate early tumor shrinkage (ETS) and deepness of response over 6-8 courses of therapy, which were assessed previously in first-line trials of anti-epidermal growth factor receptor (EGFR) monoclonal antibodies. A total of 37 patients with mCRC that was considered unresectable or borderline resectable were enrolled in the study. Patients exhibited the wild-type RAS gene, and anti-EGFR monoclonal antibodies were used as the first-line treatment in the Department of Surgical Oncology at Gifu University School of Medicine (Gifu, Japan) between January 2010 and March 2017. Tumor shrinkage and other characteristics were evaluated according to the Response Evaluation Criteria In Solid Tumors (RECIST) classifications (version 1.1). The 3-year overall survival (OS) rate was >60.0% for all cases (n=37). The mean tumor shrinkage rate in the right side of the colon according to the RECIST classifications was -11.1%, whereas that for CRC on the left side showed a statistically significant difference at -54.0% (P=0.042). In addition, the rates of OS for stable disease + progressive disease compared with partial response + complete response, and those of OS for conversion therapy compared with non-conversion therapy were significantly different (both P<0.001). Carcinoembryonic antigen (CEA) was suggested to be a possible predictive factor for convalescence due to the 50% drop in its value after the 6-8 courses of therapy. Overall, the predictive performance of ETS with respect to PFS and OS is at least as good as the standard RECIST response, with the advantage of an earlier assessment, and this may improve convalescence, with CEA as a marker in support of ETS over a clinical treatment course. In RAS wild-type patients, it is important to evaluate the rate of tumor shrinkage from the beginning of the first-line treatment until 6-8 courses of anti-EGFR monoclonal antibodies have been administered.