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Clinicopathological features, efficacy of anti-EGFR therapy, and survival outcomes in patients with BRAF non-V600 mutated metastatic colorectal cancer.

659 Background: BRAF non-V600 mutations occur in 2-3% of colorectal cancer. These mutants can be classified as RAS independent (class 2) or RAS dependent (class 3). We reported BRAF non-V600 mutations could be a negative predictive factor for anti-EGFR therapy in patients (pts) with pretreated metastatic colorectal cancer (mCRC), while mCRC pts with class 3 BRAF mutations could respond to anti-EGFR therapy because of its dependency on receptors and RAS. Methods: This study evaluates the efficacy to anti-EGFR therapy in a large cohort of pts with BRAF non-V600 mutated mCRC. Pts with mCRC referred to the participating centers from 2010 to 2017 were included. Clinicopathological features, efficacy of anti-EGFR therapy, and survival outcomes were stratified by BRAF mutational class. Results: One hundred seventeen pts with BRAF non-V600 mutated mCRC were identified. Median age was 58 years (range, 27-83), 68 pts (58%) were male, and 38 pts (33%) had right-sided tumors. Mucinous histology was seen in 11 cases (9%); concurrent RAS mutations occurred in 31 cases (27%), and 3 cases (3%) were MSI-H. Also, TP53 mutations were detected in 74 pts among 90 analyzed cases (82%). Regarding BRAF mutation subtype, 25/63/29 pts were classified as class 2/3/not reported (NR), respectively. Median OS in RAS wild-type/mutant were 44.8/34.6 months, respectively (p=0.082). The median OS in RAS wild-type pts with BRAF non-V600 mutations for class 2, 3, and NR were 25.7, 44.2, and 79.1 months, respectively (class 2 vs. 3, p=0.219). Among 40 pts treated with anti-EGFR therapy, response rates were 14%, 44%, and 40% for class 2, 3, and NR, respectively. Median PFS was 4.4, 8.3, 4.0 months for class 2, 3, and NR, respectively. Moreover, in 25 pts receiving anti-EGFR therapy as third or later line, response rate was 0%, 27%, and 50% in class 2, 3, and NR, and median PFS was 2.8, 3.7, and 4.0 months (p=0.762), respectively. Conclusions: Pts with class 2 BRAF mutations tend to have a poor prognosis compared to those with class 3 mutations. While almost half of pts with class 3 BRAF mutations responded to anti-EGFR therapy, response was rare for pts with class 2 BRAF mutations, and none achieved objective response in the third or later line.