PIK3CA mutations in breast cancer: A potential predictive marker.

639 Background: Somatic mutations in phosphoinositide-3-kinase catalytic alpha (PIK3CA) activates Akt, attenuates apoptosis and promotes tumor invasion. The common mutations E545K and H1047R confer resistance to paclitaxel in immortalized breast cancer cell lines. We screened primary breast cancers for PIK3CA mutations in the helical and catalytic domains.,Tumor samples from 61 stage I-III breast cancer patients treated with adjuvant chemo- and/or hormone therapy were examined for PIK3CA mutations E542K, E545K and H1047R by the 5-nuclease assay (TaqMan) using the ABI Prism 7900HT Sequence Detection System.,Mutations were found in 17 patients (27.9%): 6 E542K; 5 E545K; 6 H1047R. PIK3CA mutations were not associated with expression of estrogen or progesterone receptors, lymph node metastases, or ERBB2 overexpression. (See table ) Conclusions: PIK3CA mutations occur frequently in breast cancer and could be a novel predictive marker of chemoresistance and an appealing target for therapeutic inhibition, independent of hormone receptors and ERBB2 status. [Table: see text] No significant financial relationships to disclose.