The mutational spectrum of HRAS, KRAS, NRAS and FGFR3 genes in bladder cancer

Bladder cancer is one of the most common cancers worldwide. A number of genetic and epigenetic alterations have been identified in bladder tumorigenesis, including activating mutations in fibroblast growth factor receptor 3 (FGFR3) and RAS family genes. In this study, we have analysed the mutational spectrum of FGFR3 and RAS genes (HRAS, NRAS and KRAS). We have also studied the relationship between mutations. A total of 234 patients with different stages and grades were included in the present study (58 superficial low-grade, 53 superficial high-grade and 123 muscle-invasive tumours). Mutations in exons 1 and 2 of HRAS, KRAS and NRAS genes were screened by PCR and direct sequencing. The hot spot mutations in exons 7, 10 and 15 of the FGFR3 oncogene were studied by multiplex PCR and the SNaP-shot protocol. Overall, 8.97% (21/234) of samples were mutant for one of the RAS genes. Among these mutations 47.61% were detected in KRAS, 33.33% in HRAS and only 19.04% most frequent RAS mutations were KRAS p.G12C and p.G12D. The correlation between RAS mutations and tumour subgroups does not report a statistical significant association (p=0.876). The FGFR3 mutations were detected in 31.19% (73/234) of bladder tumours and were associated with low stages and grades. The study of relationship between RAS and FGFR3 genes revealed that FGFR3 mutations were mutually exclusive with RAS ones (p=10(-4)). In conclusion we retain that activated RAS and FGFR3 do not appear to be drivers in bladder cancer but the mutually exclusive relationship between RAS and FGFR3 mutations indicates a possible clonal advantage of modified signaling via a common pathway.