Phosphorylated c-Src predicts clinical outcome in triple negative breast cancers

Abstract #2076 Background: Recent in vitro evidence suggests that c-Src inhibitors may be effective in inhibiting growth of basal-type/"triple-negative" cell lines. However there is little evidence to support this in clinical specimens. Development of treatment for women with these aggressive ER, PR and HER2 negative cancers is particularly important with the lack of current effective therapies. Activation of Src family members are associated with phosphorylation at two sites Y419: the classical activation site and Y215, known to induce a 50-fold increase in activation. The aim of the current study is to assess if expression levels and/or activation of Src kinase is associated with clinical outcome measures in ER and HER2 negative human breast cancers. Methods: Tissue microarrays consisting of 172 ER and HER2 negative breast cancer tumors were constructed. Median clinical follow up was 5.9 years with 64 deaths attributed to breast cancer. Immunohistochemistry was performed using antibodies to c-Src, pSrc419 and pSrc215 (antibodies to Y419 and Y215 will detect phosphorylation of c-Src and other family members). Expression was assessed by two independent scorers. All statistical calculations were performed using SPSS 15, including Kaplan-Meier life table analysis with log rank testing of differences in breast cancer related survival. Results: Membrane expression of c-Src, pSrc419 and pSrc215 was rarely observed and was not associated with outcome. However cytoplasmic expression was frequently observed. There was a trend towards reduced survival seen with c-Src and pSrc419 overexpression. In direct contrast pSrc215 was significantly associated with increased disease specific survival and was independent on multivariate analysis. We then hypothesised that activation of c-Src via Y419 but not Y215 was driving the observed association with outcome. Indeed c-Src positive, pSrc419 positive and pSrc215 negative patients have a 25% 5yr survival rate, in comparison all other patients in the cohort had a 72% 5yr survival rate. Discussion: These results support the in vitro studies suggesting Src family members are associated with progression of triple negative breast cancers. If confirmed in a larger cohort, these results suggest that Src family members may offer a therapeutic target for triple negative cancers. However care must be taken to appropriately select patients with phosphorylation only at Y419 and not Y215. The reason why Y215 phosphorylation is asso