Retrospective pooled analyses have identified KRAS, BRAF, NRAS, and PIK3CA mutations as potentially negative predictive factors for colorectal cancer patients treated with Cetuximab (Cmab). We developed a novel kit that applies Luminex technology for the detection of mutations in KRAS codon 61, KRAS codon 146, BRAF, NRAS, and PIK3CA in a single reaction (GENOSEARCH Mu-PACK).Methods
Formalin-fixed paraffin-embedded tumor samples and clinical data of colorectal cancer patients treated with Cmab-containing regimens were collected from seven Japanese centers. KRAS, BRAF, NRAS, and PIK3CA gene statuses were determined, both by our kit and by direct-sequencing (DS). Objective response, progression-free survival (PFS), and overall survival (OS) were evaluated in subgroups determined by the mutation status.Results
A total of 82 samples were collected. The concordance rate between our kit and DS data was 98.7%. Our kit results identified 21 samples with mutations in KRAS codon 12, 13 (25.6%), 3 in KRAS codon 61 (3.7%), 2 in KRAS codon 146 (2.4%), 4 in BRAF (4.9%), 2 in NRAS (2.4%), and 4 in PIK3CA (4.9%). All of these mutations, except for PIK3CA, were mutually exclusive. The response rate for all patients in the study was 25.6%, whereas the response rate for the group of patients with all wild-type tumors was 42.0%. The median PFS values of patients with all wild-type tumors (n = 50), with KRAS codon 12, 13 mutation (n = 20), and with any of KRAS codon 61, KRAS codon 146, BRAF, NRAS, or PIK3CA mutations (n = 12) were, respectively, 6.4 months (95% CI: 3.1, 9.8), 2.1 months (95% CI: 0.8–3.5), and 1.6 months (95% CI: 1.5, 1.7) (log-rank test, P < 0.0001). The median OS values were, respectively, 15.6 months (95% CI: 11.1, 20.2), 7.9 months (95% CI: 4.8, 10.9), and 6.3 months (95% CI: 1.9, 10.7) (log-rank test, P < 0.0001).Conclusions
Patients with KRAS codon 61, KRAS codon 146, BRAF, NRAS, and PIK3CA mutations may not derive clinical benefits from Cmab, nor would patients with KRAS codon 12, 13 mutations. This newly developed detection kit is robust and practical for examining a patient's KRAS codon 61, codon 146, BRAF, NRAS, and PIK3CA gene status.