Clinical outcome in patients with metastatic colorectal cancer harboring KRAS p.G13D mutation treated with cetuximab.

448 Background: Metastatic colorectal cancer patients with KRAS codon 12 or 13 mutated tumors are presently excluded from treatment with cetuximab (Cmab). On the other hand, a few patients who have mutated KRAS status occasionally respond to Cmab. The tumors of those patients predominantly had codon 13 mutation, and all codon 13 responder have mutation of p.G13D. We now compared the efficacy of Cmab among patients with p.G13D- mutant, other KRAS mutant and KRAS wild-type colorectal cancer. Methods: The patients from 9 Japanese institutions were retrospectively collected and analyzed. All patients were refractory to fluoropyrimidine, oxaliplatin and irinotecan, and were treated with Cmab and irinotecan combination regimen. Response rate (RR), progression-free survival (PFS) and overall survival (OS) were calculated respectively according to KRAS status. Results: Ninety four patients were treated with combination therapy. Among 94 cases, 7 cases were p.G13D-mutant KRAS, 23 cases were other mutant KRAS and 63 cases were wild-type KRAS. Baseline characteristics by each subset were well-balanced. While one partial response (PR) and 4 stable diseases (SD) cases were found in 7 p.G13D-mutated cases, no PR was found in other KRAS mutated cases. Median PFS of the patients with p.G13D-mutant, other KRAS mutant and KRAS wild-type were 4.5 months (95%CI 1.7-), 2.3 months (95%CI 1.9-4.3), 4.6 months (95%CI 3.5-6.5) respectively. And median OS of the patients with p.G13D- mutant, other KRAS mutant and KRAS wild-type were 9.3months (95%CI 8.5- 11.8), 7.4 months (95%CI 4.5-9.4), 12.2 months (95%CI 8.7-19.8) respectively. Although statistical significance was not found between the two mutated groups, there are trends that the patients with p.G13D-mutant may have received better clinical benefits from Cmab than the patients with other KRAS mutant. Conclusions: Cmab may have therapeutic benefit in the patients with KRAS p.G13D-mutant colorectal cancer although further evaluation is warranted. No significant financial relationships to disclose.