The physical location of a primary tumor may be an indicator of survivor in patients with metastatic colorectal cancer (mCRC), according to results from a large retrospective study presented at the American Society of Clinical Oncology Annual Meeting in Chicago, IL (June 3-7, 2016).
Data for the study was taken from a phase 3 clinical trial of patients with mCRC who were randomly assigned to receive either bevacizumab with chemotherapy or cetuximab with chemotherapy. Investigators found no difference between the drugs, but 293 patients were found to have right-side tumors while 732 had left-side primary tumors.
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Among these patients, researchers found that those with left-side tumors had a significantly higher median overall survival than those with right-side tumors (33.3 months vs 19.4 months, respectively). The difference was most pronounced in patients who received cetuximab, where patients with left-side tumors had an overall survival of 36 months compared with 16.7 months among those with right-side tumors. In contrast, patients in the bevacizumab group had an overall survival of 31.4 months for those with tumors on the left side and 24.2 months for right-side tumor patients. Progression-free survival was found to be similar for both groups regardless of tumor location (11.5 months [left side] vs 8.9 months [right side].
In a separate analysis of 213 patients with KRAS mutations—an important factor when using cetuximab—patients with left-side tumors again survived longer (30.3 months) than those with right-side tumors (23.1 months).
Therefore, researchers concluded that primary tumor location may be an important factor in the selection of treatment for patients with mCRC.
“These findings will likely change the way we approach colorectal cancer treatment and research, even as we seek to more deeply understand the biology driving the difference in outcomes between right- and left-sided cancers,” said lead author of the study Alan P Venook, MD, of the University of California, San Francisco.
