Abstract 1606: Clinical routine massive parallel sequencing highlights clinicopathological associations of the RAS/RAF mutational module in metastatic colorectal cancer and reveals high frequency of concomitant RAS/RAF mutations

Abstract

Abstract Background: Over the past few years, massive parallel sequencing (MPS) has become reliable and cost-effective, and its use in clinical practice has become a reality. A relevant role for MPS is the prediction of response to anti-EGFR agents in metastatic colorectal cancer (mCRC), where multiple exons from KRAS, NRAS, and BRAF must be sequenced simultaneously.Patients and methods: We optimized a 14-amplicon panel to assess by MPS the exonic regions of KRAS, NRAS, BRAF, and PIK3CA from formalin-fixed, paraffin-embedded specimen-extracted DNA. We analyzed the samples of a monocentric, prospective, consecutive cohort of patients affected by mCRC collected for diagnostic and research purposes at the time of diagnosis in our referral basin.Results: Over two years, we evaluated 219 mCRC specimens. We observed an unexpected, statistically significant association of RAS mutations with sex, young age, and tumor site (right colon). We further demonstrated, by transversal validation using digital polymerase chain reaction, that concomitant mutations in the KRAS/BRAF/NRAS module are not infrequent in mCRC. As anticipated by large, whole-genome studies, RAS and PIK3CA tended to be concurrently mutated. We corroborated associations such as the higher prevalence of BRAF mutations in right mCRCtumors, in concomitance with microsatellite instability. Finally, survival analysis showed that BRAF mutants had a shorter progression-free survival compared to KRAS/NRAS mutant patients and wildtype ones upon I line treatment.Conclusions: To our knowledge, this is the first monocentric, consecutive, prospectively accrued clinical mCRC cancer cohort tested on a clinical routine basis by MPS for KRAS, NRAS, BRAF, and PIK3CA. Our study has highlighted in clinical practice findings such as the concomitance of mutations in the RAS/RAF module, the co-occurrence of RAS and PIK3CA mutations, and possible associations of gender with specific mutations. These results need clinical follow-up in the context of treatment to assess their translational relevance. Citation Format: Edoardo Isnaldi, Anna Garuti, Gabriella Cirmena, Stefano Scabini, Federica Grillo, Luca Mastracci, Lorenzo Ferrando, Roberto Murialdo, Maurizio Gallo, Christine Desmedt, Roberto Fiocca, Emanuele Romairone, Alberto Ballestrero, Gabriele Zoppoli. Clinical routine massive parallel sequencing highlights clinicopathological associations of the RAS/RAF mutational module in metastatic colorectal cancer and reveals high frequency of concomitant RAS/RAF mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1606.