RE: Primary Tumor Location as a Prognostic Factor in Metastatic Colorectal Cancer

Colorectal cancer is a group of distinct diseases rather than a homogeneous one. Fotios Loupakis et al. (1) published an interesting paper, which suggested that patients with left-sided colorectal cancers had more favorable prognosis than right side. What’s more, the authors also proposed that the efficacy of bevacizumab was independent of tumor location. The study was based on well-known clinical trials and described in reasonable detail. In our opinion, there are three points that might weaken the stringency of their study.

First, in Fotios Loupakis’ study (1), left-side cancers were defined as those of origin from descending colon, sigmoid colon, or rectum. However, descending and sigmoid colon cancers are different from rectal cancer in molecular features, treatment approaches, and prognosis (2–4). As a result, it may not be appropriate to mix left-side colon and rectum into one group. Second, although the number of metastatic sites was balanced between groups, some other important prognostic factors were unbalanced or unmentioned, including staging at diagnosis, carcinoembryonic antigen levels, number of patients who accepted R0 resection, and primary tumor resection (5). Last but not least, the author mentioned that the efficacy of bevacizumab was independent of tumor location, which in our opinion is an overambitious conclusion. In other words, the authors studied the impact of primary tumor location on patients who accepted chemotherapy, as well as patients who accepted chemotherapy plus bevacizumab. However, what they did not evaluate was the impact of bevacizumab on survival among patients grouped by the primary tumor location. We would like to suggest the authors compare survival between patients who accepted chemotherapy alone and chemotherapy plus bevacizumab in patients with right-side colon cancer, as well as left-side colon cancer and rectal cancer.