Abstract
Abstract Phosphatidylinositol-4, 5-biphosphate 3-kinase, catalytic subunit alpha (PIK3CA) is one of the most commonly mutated genes in breast cancer. But the prognostic and predictive role of PIK3CA mutations remains a matter of debate. It has been suggested that PIK3CA mutations are related to resistance to trastuzumab-based therapies, but they were also related to relatively indolent disease with better progression-free survival. Recently, circulating tumor DNA has been proposed to be a sensitive biomarker for detecting the presence of specific genetic aberrations in various cancer types, providing prognostic and predictive information. In this study, we evaluated prognostic and predictive role of PIK3CA mutations in patients with HER2-positive metastatic breast cancer treated with 1st line trastuzumab and taxane combination chemotherapy. Thirty-four patients with blood samples obtained before 1st line trastuzumab and taxane combination chemotherapy were included in the study. We analyzed two PIK3CA hotspot mutations (E545K, H1047R) in ctDNA by digital droplet PCR (RaindropTM). The samples were collected from April 2005 to December 2011, centrifuged and stored as plasma, and were analyzed in 2015, after 4-10 years of storage period. Median age was 47 years (range: 31 to 75 years), and histologic type of cancer was ductal carcinoma in all cases. PIK3CA mutations were detected in 21 (61.8%) of 34 patients. Patients with mutated PIK3CA in ctDNA had longer progression-free survival (PIK3CA wild type vs mutant, 11.0 months vs 22.0 months; P = 0.013). In hormone receptor positive group, patients with mutated PIK3CA had longer progression-free survival (PIK3CA wild type vs mutant, 12 months vs 18 months, P=0.17). Patients with PIK3CA mutations had a lower objective response rate than patients with wild-type, but there was no statistical significance (CR+PR; PIK3CA wild type vs mutant, 84.6% vs 66.7%, P=0.43). There was no significant difference in response rate (P = 0.48) or PIK3CA mutational status (P = 0.44) according to hormonal receptor status (estrogen receptor and/or progesterone receptor). In conclusion, PIK3CA mutations were frequently detected by digital PCR from ctDNA of patients with HER2-positive breast cancer and they were related to significantly better PFS. We plan to analyze the PIK3CA mutation status in matched tumor tissue. Citation Format: Lim J, Lee K-H, Min A, Kim S-G, Kim J-E, Kim T-Y, Han S-W, Oh D-Y, Kim T-Y, Lim S-A. Prognostic role of PIK3CA mutational status in circulating tumor DNA (ctDNA) from HER2-positive metastatic breast cancer patients [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-02-05.
Published Version
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