601PCorrelation between p53 expression and clinical outcome in RAS/BRAF wild type metastatic colorectal cancer patients receiving later-line irinotecan-cetuximab

Abstract Background Preclinical and clinical data support that p53 might modulate the EGFR activity and as a consequence it might influence response/resistance to anti-EGFR monoclonal antibodies. However, the association between p53 status and clinical outcome has not been clarified yet. In our study we evaluated the role of p53 expression in RAS/BRAF wild type (WT) metastatic colorectal (mCRC) patients (pts) receiving irinotecan-cetuximab by using a validation cohort. Methods p53 immunohistochemical expression was retrospectively analysed in tumour samples of RAS/BRAF WT mCRC pts treated with second-third line irinotecan-cetuximab. Our aim was to evaluate the correlation between p53 expression and OS, PFS and RR. Statistical analysis was performed with the MedCalc package. Survival distribution was assessed by the Kaplan-Meyer method and comparison of survival curves was performed with log-rank test. Results Globally 120 RAS/BRAF WT mCRC pts were included in our analysis, 88 in the exploratory cohort and 32 in the validation cohort. 36/88 and 14/32 pts had p53 normal expression, whereas 52/88 and 18/32 showed p53 overexpression. In the exploratory cohort, RR was 61.1% in pts with p53 normal expression versus (vs) 3.8% in pts overexpressing p53 (p