Analysis of PIK3CA Mutation Concordance and Frequency in Primary and Different Distant Metastatic Sites in Breast Cancer

Abstract

Purpose The purpose of this study was to investigate the concordance rate of <i>PIK3CA</i> mutations between primary and matched distant metastatic sites in patients with breast cancer and to verify whether there are differences in the frequency of <i>PIK3CA</i> hotspot mutations depending on the metastatic sites involved.Materials and Methods Archived formalin-fixed paraffin-embedded (FFPE) specimens of primary breast and matched distant metastatic tumors were retrospectively obtained for 49 patients. Additionally, 40 archived FFPE specimens were independently collected from different breast cancer metastatic sites, which were limited to three common sites: the liver, brain, and lung. <i>PIK3CA</i> mutations were analyzed using droplet digital PCR, including hotspots involving exons 9 and 20. Results After analysis of 49 breast tumors with matched metastasis sites, 87.8% showed concordance in <i>PIK3CA</i> mutation status. According to <i>PIK3CA</i> hotspot mutation testing in 89 cases of breast cancer metastatic sites, the proportion of <i>PIK3CA</i> mutations at sites of metastasis involving the liver, brain, and lung was 37.5%, 28.6%, and 42.9%, respectively, which did not result in statistical significance. Conclusion The high concordance of <i>PIK3CA</i> mutation status between primary and matched metastasis sites suggests that metastatic sites, regardless of the metastatic organ, could be considered sample sources for <i>PIK3CA</i> mutation testing for improved therapeutic strategies in patients with metastatic breast cancer.