A retrospective analysis of cetuximab efficacy based on the comprehensive RAS/RAF mutation profiles of colorectal cancer

Background In colorectal cancer the most frequently analyzed markers are RAS/RAF mutations which have negative predictive role for anti-EGFR antibody therapy. Although the hotspot mutations of the K- and NRAS exon 2-4 are well defined, the predictive role of rare mutations of other codons are questionable and the current guidelines are less precise in this respect. Methods We have retrospectively re-analyzed the full spectrum of RAS/RAF mutations by next-generation sequencing (NGS) in a small cohort of nineteen cetuximab treated metastatic colorectal cancer patients whose enrollment was based on KRAS exon 2 mutation analysis. Results We have detected 13 rare RAS/RAF mutations where 5 occurred together with hotspot (HSP) mutations. In the five non-HSP mutant cases we have detected 8 rare/non-HSP RAS/RAF mutations: KRAS-E37.,C51Y, NRAS-D57N,E62K,G60E/V14I, HRAS-P34L and BRAF-G464R. Kaplan-Meier analysis indicated that the progression free survival (PFS) of non-HSP cases ran parallel with wild type (WT) cases separately from the HSP mutant cases without statistical significance (p = 0.156). However, the combination of WT group with non-HSP cases resulted in a near significant survival difference from HSP cases (p = 0.057, HR = 3.501). Kaplan-Meier analysis of the overall survival (OS) again demonstrated that the survival curve of WT cases ran parallel with non-HSP cases, clearly separated from the HSP cases (p = 0.024). Overall survival of WT cases was significantly different as compared to HSP cases (p = 0.005) with HR of 6.362 (CI 1.496–27.055) as expected, while it was not statistically different from non-HSP cases (p = 0.092) with a HR of 0.891 (CI 0.248–3.205). Conclusion In this small retrospective study we showed that the analyzed non-HSP mutations of RAS/RAF in colorectal cancer treated with cetuximab do not have negative effect on the efficacy. Since our cohort is very small and do not have accordingly the necessary statistical power of the survival analyses, therefore can only be considered as hypothesis generating one of the issue of the predictive role of non-hotspot RAS mutations on cetuximab efficacy.