Clinical outcome of Japanese metastatic colorectal cancer patients harbouring the KRAS p.G13D mutation treated with cetuximab + irinotecan.

OBJECTIVE: Metastatic colorectal cancer with KRAS codon 12 or 13 mutations is not currently treated with anti-epidermal growth factor antibodies. A recent retrospective study in Western countries raised the possibility that KRAS p.G13D mutation may not be absolutely predictive of non-response compared with other KRAS mutations from the findings of longer overall survival and progression-free survival following cetuximab treatment. We retrospectively investigated the relationship between KRAS status and cetuximab efficacy among Japanese patients.
METHODS: Data of 109 patients from nine institutions in Japan were retrospectively analysed. All patients were refractory or intolerant to fluoropyrimidine, oxaliplatin and irinotecan, and they were treated with a cetuximab + irinotecan regimen. The response rate, disease control rate, progression-free survival and overall survival were compared according to KRAS status.
RESULTS: Overall, 76 (70%), 7 (6%) and 26 (24%) patients had KRAS wild-type, KRAS p.G13D and other KRAS mutations. Their various parameters were as follows: response rate: 30% (23/76), 14% (1/7) and 0% (0/26); disease control rate: 71% (54/76), 71% (5/7) and 54% (14/26); median progression-free survival: 4.6 months (95% confidence interval, 2.8-6.3), 4.1 months (0-9.9) and 2.1 months (1.5-2.8); and median overall survival: 11.2 months (6.4-16.0), 8.5 months (5.3-11.8) and 6.8 months (4.1-9.6), respectively.
CONCLUSIONS: Although no statistically significant difference in progression-free survival or overall survival was observed between KRAS p.G13D-mutant and other mutant tumours, the disease control rate was higher in KRAS p.G13D-mutant patients and a partial response was observed in one such patient. Our study suggested that cetuximab showed some activity in KRAS p.G13D-mutant colorectal cancer patients. Further research is warranted.