Morphological response and tumor shrinkage as predictive factors in metastatic colorectal cancer treated with first-line capecitabine, oxaliplatin, and bevacizumab.

Background: Morphologic response (MR) is a novel chemotherapeutic efficacy predictor of solid tumors, especially those treated with anti-vascular endothelial growth factor antibodies. Nevertheless, the importance of systemic chemotherapy MR for colorectal liver metastases (CLM) remains unclear. We aimed to evaluate the usefulness of MR as a factor associated with the therapeutic effects of chemotherapy plus bevacizumab for initially unresectable CLM cases.

Methods: We retrospectively evaluated the associations between MR and/or Response Evaluation Criteria in Solid Tumors (RECIST), progression-free survival (PFS), and overall survival (OS) in patients who received first-line capecitabine, oxaliplatin, and bevacizumab treatment for initially unresectable CLM using multivariate analysis. Patients who showed a complete or partial response based on the RECIST, or an optimal response based on MR, were defined as "responders."

Results: Ninety-two patients were examined, including 31 (33%) patients who responded optimally. PFS and OS estimates were comparable in MR responders and non-responders (13.6 vs. 11.6 months, p = 0.47; 26.6 vs. 24.6 months, p = 0.21, respectively). RECIST responders showed better PFS and OS than non-responders (14.8 vs. 8.6 months, p < 0.01; 30.7 vs. 17.8 months, p < 0.01, respectively). The median PFS and OS estimates of MR and RECIST responders were better than those of single responders or non-responders (p < 0.01). Histological type and RECIST response were independently associated with PFS and OS.

Conclusion: MR predicts neither PFS nor OS; nevertheless, it may be useful when combined with the RECIST. The Ethics Committee of The Cancer Institute Hospital of JFCR approved this study in 2017 (No. 2017-GA-1123): retrospectively registered.