FOLFIRI with cetuximab or bevacizumab in RAS wild-type metastatic colorectal cancer: Refining first-line treatment selection by combining clinical parameters: A post hoc analysis of the randomized open-label phase III trial FIRE-3/AIO KRK0306

Abstract

Background: Primary tumor sidedness (PTS) with discrimination of left-sided (LC) and right-sided tumors (RC) guides patient selection for targeted first-line therapy in RAS wild-type (RAS-WT) metastatic colorectal cancer (mCRC). This study assessed the hypothesis whether considering PTS with additional clinical parameters better predicts the treatment benefit of targeted first-line treatment.

Methods: In FIRE-3, first-line treatment with folinic acid, fluorouracil and irinotecan (FOLFIRI) plus cetuximab (FOLFIRI/Cet) was compared to FOLFIRI plus bevacizumab (FOLFIRI/Bev) in patients with RAS-WT mCRC and unresectable metastasis. We evaluated whether combining PTS with number of metastatic sites (NOM), liver-limited disease status (LLD), age, sex, or carcinoembryonic antigen level (CEA) better predicts treatment benefit regarding overall survival (OS). Here, Cox regression models with second-order interactions were applied. Further, the results were validated by policy learning and Lasso regression analysis.

Findings: Among 400 RAS-WT mCRC patients, combining PTS with LLD status in a Cox regression model outperformed PTS alone for predicted treatment benefit (P = 0·005; c‑index=0·603). Significant OS benefit from FOLFIRI/Cet over FOLFIRI/Bev was observed in LC/non-LLD patients (HR=0·62; 95 %-confidence interval [CI]=0·46-0·82; P = 0·002), but mitigated in LC/LLD patients (HR=0·83; 95 %-CI=0·53-1·29; P = 0·400). In RC/non-LLD patients, FOLFIRI/Bev demonstrated a significant OS advantage over FOLFIRI/Cet (HR=2·09; 95 %‑CI=1·20-3·63; P = 0·010). However, RC/LLD patients showed potential benefit from FOLFIRI/Cet, though not statistically significant (HR=0·59; 95 %-CI=0·25-1·39; P = 0·218).

Interpretation: Incorporating PTS and LLD status might improve selection of targeted first-line treatment in RAS-WT mCRC patients. FOLFIRI/Cet appears to be particularly beneficial for LC/non-LLD patients with mitigated benefit in patients with LC/LLD. In contrast, FOLFIRI/Bev is significantly favoured over FOLFIRI/Cet in patients with RC/non-LLD. Notably, RC/LLD patients may still benefit from anti-EGFR therapy despite right-sided primary tumor. These results are hypothesis-generating and warrant further validation.

Keywords: Bevacizumab; Biomarker combination; Cetuximab; Comprehensive statistical modeling; FOLFIRI; Liver-limited disease; Metastatic colorectal cancer; Metastatic pattern; Predictive biomarker; Primary tumor sidedness.