Impact of second-line and later cetuximab-containing therapy and KRAS genotypes in patients with metastatic colorectal cancer: a multicenter study in Japan

Purposes This retrospective study evaluated the treatment outcomes and clinical relevance of the KRAS mutation status in Japanese metastatic colorectal cancer patients treated with second-line and later cetuximab-containing therapy. Methods The subjects comprised 65 patients with metastatic colorectal cancer who received cetuximab-containing therapy. At the start of cetuximab-containing therapy, the KRAS mutation status had been proven to be wild type in 12 patients. Tumors were retrospectively screened for KRAS mutations using direct sequencing. Results A detailed analysis revealed the presence of 24 wild-type (57.1 %) and 18 mutant tumors (42.9 %). Grade 3–4 neutropenia and anemia were observed in 21 (32.3 %) and nine (13.8 %) patients, respectively. An acne-like rash was observed in 50 patients (76.9 %), and among them three patients (4.6 %) experienced a Grade 3 rash. A KRAS mutation was associated with resistance to cetuximab-containing treatment (11.1 vs. 41.7 % responders among 18 mutant and 36 wild-type patients, respectively; P = 0.03). A KRAS mutation was also associated with poorer survival (MST: 6.9 vs. 14.1 months in 18 mutant and 36 wild-type patients, respectively; P = 0.018). Conclusions The present results indicated the clinical relevance of KRAS mutations in predicting the efficacy of cetuximab-containing therapy for metastatic colorectal patients in the Japanese population.