PIK3CAtesting in hormone receptor-positive/HER2-negative metastatic breast cancer: real-world data from Italian molecular pathology laboratories

Introduction:PIK3CAgene mutations occur in approximately 40% of hormone receptor-positive/HER2-negative (HR+/HER2−) metastatic breast cancers (MBCs), electing them to targeted therapy. Testing PIK3CAstatus is complex due to selection of biological specimen and testing method. Materials & methods:This work investigates real-life experience on PIK3CAtesting in HR+/HER2−MBC. Clinical, technical and molecular data on PIK3CAtesting were collected from two referral laboratories. Additionally, the results of a nationwide PIK3CAsurvey involving 116 institutions were assessed. Results:Overall, n = 35 MBCs were PIK3CA-mutated, with mutations mostly occurring in exons 9 (n = 19; 51.4%) and 20 (n = 15; 40.5%). The nationwide survey revealed significant variability across laboratories in terms of sampling methodology, technical assessment and clinical report signing healthcare figures for PIK3CAmolecular testing in diagnostic routine practice. Conclusion:This study provides insights into the real-world routine of PIK3CAtesting in HR+/HER2−MBC and highlights the need for standardization and networking in predictive pathology.