The addition of bevacizumab to cytotoxic (toxic to cells) chemotherapy is associated with improved survival in patients with stage IV colorectal cancer and higher pathologic response rates in patients undergoing resection (surgical removal) of colorectal liver metastases. "Recently, pathologic response to preoperative chemotherapy has been shown to correlate with improved survival and has been proposed as a new outcome end point after resection of colorectal liver metastases. To date, a noninvasive method of predicting pathologic response to chemotherapy in colorectal liver metastases, particularly biologic agents, is lacking," the authors write. They add that it has been observed that after bevacizumab-containing therapy, colorectal liver metastases tend not only to decrease in size but also to undergo unique morphologic (form and structure) changes on CT.
Yun Shin Chun, M.D., of the University of Texas M. D. Anderson Cancer Center, Houston, and colleagues conducted a study to validate tumor response criteria that are based on morphologic changes observed on CT in patients with colorectal liver metastases treated with bevacizumab-containing chemotherapy regimens. The researchers analyzed a total of 234 colorectal liver metastases from 50 patients who underwent hepatic resection (removal of tumors involving the liver) after preoperative chemotherapy that included bevacizumab, from 2004 to 2007; date of last follow-up was March 2008. All patients underwent routine contrast-enhanced CT at the start and end of preoperative therapy. Radiologists evaluated images for morphologic response, based on metastases changing from heterogeneous masses with ill-defined margins into homogeneous lesions with sharp borders. These criteria were validated with a separate group of 82 patients with unresectable (unable to be removed by surgery) colorectal liver metastases treated with bevacizumab-containing chemotherapy.
The researchers found that "morphologic criteria correlated strongly with the percentage of residual tumor cells and also with pathologic response stratified as complete, major, or minor using 50 percent residual tumor cells as the cutoff value between major and minor pathologic response. Optimal morphologic response to preoperative therapy translated into a survival benefit after hepatic resection. In a separate validation cohort of patients with unresectable colorectal liver metastases, response by morphologic criteria was also associated with improved overall survival."
The authors add that although the sample size in the surgical group was small, "these results highlight the importance of response rather than baseline clinical factors in determining patient outcome after liver resection."
"... our results indicate that morphologic response may be a useful, noninvasive surrogate marker of pathologic response and improved survival in patients with colorectal liver metastases receiving a bevacizumab-containing regimen. It provides complementary information to traditional size-based criteria in assessing CT response to bevacizumab in colorectal liver metastases."