K-RAS codon 13 mutation in advanced colorectal cancer: A single-center retrospective study investigating prognostic outcomes and treatment strategies

633

Background: Ras genes are markers of resistance to anti-EGFR therapies. Emerging evidences suggest that each mutation, independently from its predictive role of response/resistance to specific treatments, may be expression of different diseases with different biologic behaviours. We collected data of mCRC patients harbouring K-Ras codon 13 mutation to evaluate response to therapy, PFS and OS. Methods: We retrospectively collected data of advanced colorectal cancer patients harbouring K-Ras codon 13 mutation treated at our Institution between 2004 and 2014. Results: A total of n.33 K-Ras codon 13 mutated patients were analysed. N.24 patients (72,7%) had synchronous metastatic disease. None of the patients received anti-EGFR treatment, while n.25 patients received anti-VEGF agent bevacizumab in association to chemotherapy with fluoropirimidines plus oxaliplatin and/or irinotecan (n.21 as frontline therapy, n.4 in second line). ORR was 51,5% (17/33) on first-line therapy, 22,2% (6/27) on second-line therapy and 16,6% (2/12) on third-line therapy. Median PFS was 14,1 months after first-line therapy, 9,3 months after second-line therapy, 6,4 months after third-line therapy. Median OS was 35,5 months (events: 19/33). N.14 patients received metastases surgery with radical intent. OS in this population has not been reached yet at a median follow-up of 38 months, even though all patients had a relapse. OS among patients undergone to systemic only strategy was 31 months. Conclusions: At our knowledge, this is the first report suggesting a favourable prognosis for K-ras codon 13 mutated patients, with a median overall survival even superior to pan-RAS wild-type patients. Indeed, the high percentage of advanced patients at diagnosis (72.7%), the high responsiveness to chemotherapy even in third line, the high percentage of patients converted to surgery (42.4%) in an unselected population, together with the high risk or relapse after surgery, suggest K-ras codon 13 mutated disease is probably a biologically aggressive disease. Nevertheless our data prompt that these patients may benefit aggressive strategies of treatment and multidisciplinary evaluation.