Clinical and Pathologic Characteristics of Patients with PI3K-mutant Breast Cancers.

8 Background: Mutations in PIK3CA are the most common somatic alterations in breast cancer and represent a potentially useful therapeutic target. As more PI3K pathway inhibitors enter the clinical arena, it is important to understand the characteristics of patients harboring mutations. This study seeks to identify the clinico/pathological characteristics of PI3K mutant breast cancers in patients evaluated at Vanderbilt University Medical Center. Methods: Molecular profiling (SNaPShot) was used to detect mutations in three genes in the PI3K pathway (PIK3CA, PTEN, AKT1). Electronic medical records of breast cancer patients whose tumors underwent testing from June 2010 to January 2013 were reviewed. PI3K mutation rates, histological tumor grade, receptor status (ER/PR/HER2), and recurrence-free survival were tabulated. Results: Three hundred evaluable tests were identified, with PI3K mutations detected in 83/300 (28%). Patients with PI3K mutations were more likely to be ER/PR positive (73% vs. 48%; p<0.001) and less likely to be HER2 positive (6.0% vs. 20.7%, p=0.0022). Only 6/83 patients (7.2%) with triple negative cancers harbored PI3K mutations. 32% of patients with PI3K mutations participated in clinical trials, versus 25% without. Conclusions: Tumors with PI3K mutations were more likely to be ER/PR positive, of intermediate grade, and associated with longer recurrence-free survival. Patients with PI3K mutations were more likely to participate in clinical trials. These data and the potential eligibility of patients harboring mutations for clinical trials support the prognostic and clinical utility of SNaPShot testing for all breast cancer patients at a tertiary care center. [Table: see text]