Differential Tumor Response and Conversion Outcomes Associated with First-Line Biologic Strategies in Liver-Limited RAS Wild-Type Metastatic Colorectal Cancer.

Background

Anti-EGFR therapy is widely used as first-line treatment for RAS wild-type metastatic colorectal cancer (mCRC), particularly in patients with left-sided tumors. In liver-limited disease, maximizing tumor shrinkage may facilitate conversion to resectability; however, comparative real-world evidence among panitumumab, cetuximab, and bevacizumab remains limited. This study aimed to compare the clinical outcomes of these biologic agents in patients with RAS wild-type mCRC.

Methods

We retrospectively analyzed 241 patients with RAS wild-type mCRC treated with first-line chemotherapy plus panitumumab (n = 76), cetuximab (n = 80), or bevacizumab (n = 85) between 2016 and 2024. Outcomes included depth of response (DpR), objective response rate (ORR), disease control rate (DCR), conversion surgery rate, progression-free survival (PFS), and overall survival (OS).

Results

Overall, panitumumab demonstrated superior tumor response, achieving the highest ORR (69.7%) and conversion surgery rate (34.2%), although PFS and OS were comparable among treatment groups. In patients with liver-limited disease, panitumumab was associated with a higher conversion surgery rate than bevacizumab (50.0% vs. 19.4%) and a trend toward longer OS. Right-sided primary tumors and BRAF mutation remained independent predictors of poorer OS.

Conclusions

Panitumumab-based therapy was associated with deeper tumor shrinkage and higher conversion rates, particularly in liver-limited mCRC. These findings suggest that greater cytoreduction may increase opportunities for local treatment in selected patients. However, given the retrospective nature of the study, the findings should be considered hypothesis-generating and require prospective validation.