Mutation of PI3KCA in post-menopausal women with breast cancer and response to RAD001 treatment

Abstract #4063 Background: The activation of the PI3K-AKT pathway produces abnormalities in cell growth, proliferation and survival in a number of tumour types. PIK3CA (phosphoinositide-3-kinase, catalytic, alpha polypeptide) mutations have been described in a significant proportion of breast cancers and may predict response to treatment with inhibitors of this pathway. RAD001 (everolimus) is a rapamycin derivative that inhibits mTOR and its downstream substrates and has shown promising results in Phase I studies. The aim of this study was to assess the PI3KCA mutational status in post-menopausal women with breast cancer and to relate this to response following RAD001 treatment using a multiplex real-time PCR assay by DxS Ltd. Materials & Methods: 32 post-menopausal women with early breast cancer were treated with 5mg RAD001 pre-operative treatment daily for 14 days prior to primary surgery. 25 patients completed treatment, 6 withdrew and 1 did not start medication. Biopsies were taken at diagnosis and at surgery from the 31 patients who received RAD001 and embedded in paraffin. Pre- and post-treatment biopsies were available for the analysis of biological response markers, including changes in proliferation (Ki67) and phospho-AKT (s473) by immunohistochemistry (Macaskill et al., 2006: Breast Cancer Research & Treatment: 100: S1: S286). 15 patients were classified as responders to RAD001 and 10 patients non-responders (responders were defined by a fall in % Ki-67 positive cells). Post-treatment biopsies were available for evaluation of PI3KCA mutational status. DNA was extracted from post-treatment paraffin-embedded tissues and analysed for the 3 most commonly occurring PIK3CA mutations (H1047R, E542K, E545K) using a multiplex real-time PCR assay (DxS Ltd; Board et al., 2008: Clinical Chemistry: 54:4: 757-760). Results: 8/31 (25.8%) DNA samples were found to contain PI3KCA mutations: 5 - E545K; 2 - H1047R; 1 – E542K. Although cytoplasmic phospho-AKT expression was higher in pre-treatment tumours containing PI3KCA mutations than in those without detected mutations (median histoscore - 113.8 and 70, respectively; interquartile range – 94.4 and 88, respectively), the difference was not statistically significant. 5 mutations were found in tumours from 25 patients who completed treatment. 2/15 (13%) responders and 3/10 (30%) non-responders exhibited PI3KCA mutations. However, no significant association between PI3KCA mutations and response was observed. Disc