The first experience of pik3ca testing in clinical hospital center split-what our results are?

Introduction: Breast cancer is the most commonly diagnosed cancer in women worldwide. It represents 24.5% of all cancers in women with estimated 684,996 deaths from breast cancer in 2020. More than 80% of breast cancer is classified as hormone receptor-positive (HR+) breast cancer. PIK3CA mutations occur in approximately 40% of patients with HR +, human epidermal growth factor receptor 2 (HER2)-negative breast cancer. Endocrine therapy, with or without cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor is the standard treatment for patients with HR-positive, HER2-negative advanced breast cancer. However, acquired resistance to endocrine-based therapy still remains a challenge. Moreover, the truth is that breast cancer outcomes lie in the treatment opportunities as well as system organization. Recently, PIK3CA inhibitor alpelisib became a new standard of care for a second line therapy. Its penetration in the everyday care depends on diagnostic of the biomarker-PIK3CA mutation. Here, we describe the first experience of ours in the process of diagnostics of PIK3CA mutation on the cohort of our advanced HR+, HER2-breast cancer patients. Methods: We did a retrospective analysis of data from all patients with HR+, HER2-metastatic breast cancer who were tested on presence of PIK3CA mutation in Clinical Hospital Split until December 2020. The cobas® PIK3CA Mutation Test was used. This is a real-time polymerase chain reaction (PCR) test used to identify patients with advanced or metastatic breast cancer with PIK3CA mutation. Results: From September 2019 until December 2020, we have tested 50 patients on presence of PIK3CA mutation. In all cases PCR method was used and the sample was archival tissue. Only two of all tested patients were male and the rest were female. The average age of patients was 61.13 years. The eldest patient was 81 and the youngest 32 years old at the time they were tested. The PIK3CA mutation was established in 21/50 (42%) of patients. Determined hotspot mutations were: E545 in 3/21 (14.28%), E545X in 4/21 (19.04%), E542 in 2/21 (9.53%), E542K in 2/21 (9.53%), H1047 in 2/21 (9.53%), H1047X in 4/21 (19.04%), N345K in 2/21 (9.53%) cases. In two cases (2/21, 9.53%) hotspot mutations H1047X and N345K were presented concurrently. Conclusion: Our results coincide with data from previous world studies. In our hands PIK3CA testing proves to be easily established and run. Given the situation with COVID-19 pandemic, the number of tested patients is not overly high. Additional efforts are needed to fully state testing and to test as many patients as possible so that patients who result positive could potentially have benefits from therapies directed against PIK3CA.