Evaluation of circulating tumor DNA as a prognostic and predictive biomarker in BRAF V600E mutated colorectal cancer-results from the FIRE-4.5 study

The randomized FIRE-4.5 (AIO KRK0116) trial evaluated first-line therapy with FOLFOXIRI (folinic acid, fluorouracil, oxaliplatin, and irinotecan) combined with either cetuximab or bevacizumab in patients with BRAF V600E-mutant metastatic colorectal cancer (mCRC). This trial included a prospective translational study analyzing cell-free circulating tumor DNA (ctDNA) in plasma to assess its potential for guiding clinical decision-making.

FIRE-4.5 enrolled mCRC patients with BRAF V600E mutations confirmed by tissue-based testing. Liquid biopsies (LBs) were collected at baseline (pre-treatment) and during therapy. Digital droplet PCR (ddPCR) was used to detect BRAF mutations, while the in vitro diagnostics (IVD)-certified ONCOBEAM RAS procedure was employed for RAS mutation analysis. Among 66 patients with ctDNA analyzable at baseline, 26% (17/66) showed no detectable BRAF V600E mutations. These patients experienced significantly longer progression-free survival (PFS: 13.2 vs. 6.5 months; HR 0.47; P = 0.014) and overall survival (OS: 36.8 vs. 13.2 months; HR 0.35; P = 0.02) compared to patients with detectable BRAF V600E mutations.

For patients with detectable BRAF mutations, FOLFOXIRI plus bevacizumab demonstrated superior efficacy, with improved PFS (10.4 vs. 5.7 months; HR 0.4; P = 0.009) and OS (16.6 vs. 11.6 months; HR 0.5; P = 0.15). In contrast, no significant benefit was observed in BRAF wild-type patients. Follow-up LBs were available for 51 patients, revealing that 36% (18/51) transitioned from BRAF V600E mutant to BRAF wild-type status during therapy. These 5-Fluorouracil patients had significantly improved PFS (8.6 vs. 2.3 months; P = 0.0002) and OS (17.4 vs. 5.1 months; P < 0.0001) compared to those with stable or increased mutational allele frequency (12%, 6/51). They also achieved a higher disease control rate (89% vs. 20%; P = 0.008).

In summary, ctDNA analysis via liquid biopsy provides valuable insights and may support treatment optimization in patients with BRAF V600E-mutated mCRC.