NEW YORK (Reuters Health) – Bevacizumab appears to be most effective for metastatic colorectal cancer when the primary tumor originates distally, according to a Danish study.

However, the researchers caution, “Because of the retrospective and exploratory nature of the present study, this finding should be interpreted as hypothesis-generating only, and it needs to be validated in data from completed randomized trials.”

No prognostic markers are currently available to help in the selection of patients who are likely to benefit from treatment of bevacizumab, point out the authors of the report in the Annals of Oncology online July 17. However, they note, expression of VEGF (bevacizumab’s target) has been shown to be higher in tumors from the distal colon than those in the proximal colon.

This prompted Dr. Mogens Karsbol Boisen, with Copenhagen University Hospital in Herlev, and colleagues to investigate the impact of the primary tumor location on outcomes in 880 patients with metastatic colorectal cancer (mCRC) treated with first-line capecitabine and oxaliplatin (CAPEOX) with or without bevacizumab.

Among patients who received CAPEOX and bevacizumab, median progression-free survival was significantly higher for patients with tumors arising in the sigmoid colon and rectum (9.3 months) compared to those with tumors originating in the cecum and as far as the descending colon (7.2 months), which translated to a hazard ratio of 0.68.

Corresponding figures for median overall survival were also significantly different at 23.5 versus 13.0 months, respectively, (HR 0.47), the team found.

On the other hand, primary tumor location had no effect on survival among patients who received only CAPEOX.

“The addition of bevacizumab to CAPEOX in the first-line treatment of patients with mCRC may primarily benefit patients with primary tumors originating in the rectum and sigmoid colon,” Dr. Boisen and colleagues conclude.

The authors acknowledge the limitations of the study. “On the other hand,” they comment. “the difference in outcome we observe seems unequivocal and the effect is large, which makes it less likely to be a chance finding.”

SOURCE: Primary tumor location and bevacizumab effectiveness in patients with metastatic colorectal cancer
Ann Oncol 2013.