BRAF-mutant metastatic colorectal cancer: Prognostic and predictive value of primary tumor location-A pooled analysis of the AIO studies FIRE-1, CIOX, XELAVIRI, FIRE-3, and VOLFI.

3576 Background: Primary tumor location (PTL: left vs. right) is an established prognostic marker in metastatic colorectal cancer (mCRC) and has predictive impact for anti-EGFR antibody (mAb) efficacy in patients with RAS ( KRAS and NRAS) wild-type (WT) mCRC. This analysis of five pooled studies evaluates PTL as a prognostic and - concerning anti-EGFR mAb efficacy - predictive marker in BRAF V600E-mutant/ RAS WT and mCRC. Methods: The analysis is based on individual patient data of five pooled 1st-line studies with varying treatment strategies: the pooled population comprises of BRAF V600E-mutant/ RAS WT ( BRAFmt) mCRC with known PTL. For analysis, treatment was stratified into two groups: treated with or without anti-EGFR mAb. Dichotomous variables (overall response rate, ORR; characteristics) were compared by Chi-Square or Fisher’s exact test and time-to event endpoints (progressive-free survival, PFS; overall survival, OS) by Kaplan-Meier method, log rank test and Cox regression. Results: Of 102 patients (pts) with BRAFmt mCRC, 55 pts (54%) presented with right-sided primary tumors (RPT), 47 (46%) presented with left-sided primary tumors (LPT). Pts with RPT were more likely to be female ( p= 0.04). ORR was inferior in RPT compared to LPT (35% vs. 55%; p= 0.04). No difference was seen in PFS (HR 0.8 (95% CI 0.6-1.3; p= 0.32) or OS (HR 0.8; 95% CI 0.8-1.3; p= 0.46). In male pts PTL trended to be associated with longer OS (HR 0.6; 95% CI 0.3-1.0; p= 0.06). 25 pts with RPT (45%) and 21 with LPT (45%) received anti-EGFR mAb. In pts with LPT anti-EGFR mAb based treatment was associated with higher ORR (81% vs. 35%; p< 0.01). No effect was seen in RPT (ORR 35% vs. 36%; p= 0.82). Anti-EGFR mAb treatment resulted in inferior PFS in RPT (HR 2.0; 95% CI 1.1-3.5; p= 0.02) and showed a trend towards improved PFS in LPT (HR 0.6; 95% CI 0.3-1.1; p= 0.11). Pts with RPT had a worse OS when treated with anti-EGFR mAb (HR 1.8; 95% CI 1.0-3.1; p= 0.05), whereas pts with LPT appeared to have a favorable outcome when treated with an anti-EGFR mAb containing regimen (HR 0.4; 95% CI 0.2-0.7; p< 0.01). Conclusions: This exploratory analysis of five studies suggests that PTL has limited prognostic impact in BRAFmt mCRC but might carry predictive information regarding anti-EGFR mAb efficacy in a 1st-line treatment setting. Further prospective studies are needed to validate these results and to grasp the differences in the heterogeneous group of BRAFmt pts. Clinical trial information: FIRE-1 was before mandatory registration, NCT00254137, NCT00433927, NCT01249638, NCT01328171.