Results of a retrospective study on the efficacy and safety of alpelisib in patients with HR+/HER2- metastatic breast cancer in real-world clinical practice.

e13058 Background: The combination of alpelisib and fulvestrant is an optimal therapy option for patients with hormone receptor-positive (HR+), HER2-negative (HER2–) metastatic breast cancer with PIK3CA gene mutations. The aim of this work to retrospectively analyze the efficacy and safety of alpelisib in real-world clinical practice in patients with pre-treated luminal HER2– negative metastatic breast cancer. Methods: The study included an analysis of 33 patients with widespread luminal HER2- negative breast cancer with detected PIK3CA gene mutation. The median age was 57 ± 13 months (95% CI 52-62). In 12 (36.4%) patients, the PIK3CA gene mutation was detected in exon 9, and in 21 (63.6%) – in exon 20. Alpelisib was prescribed to pre-treated patients in different lines. Most women (32/33; 97%) had received ET combined regimens with CDK4/6 inhibitors before starting alpelisib therapy: 14 (42.4%) patients underwent palbociclib therapy in combination with fulvestrant; 4 (12.1%) – palbociclib with aromatase inhibitors; 13 (39.5%) – ribociclib in combination with fulvestrant; 1 (3.0%) – ribociclib with aromatase inhibitors. It is important to note that 63.6% of patients had previous progression on fulvestrant monotherapy and 72.7% on aromatase inhibitor therapy. Patients with luminal B-subtype of breast cancer dominated - 72.7% (24/33). Results: The median overall survival (OS) in this study was 14 ± 2.5 months (95% CI: 9-18.9), and the median progression-free survival (PFS) was 6 ± 2.7 months (95% CI: 0.7-11.3). The rate of objective response was 30.3%, and prolonged disease stabilization was observed in 24.2% of cases. Prognostic factors were brain metastases (increasing the risk of death by 18 times) and discontinuation of the drug for any reason (increasing the risk of death by 8 times). It should be noted that the main reason for discontinuation or disruption of the drug's timing was unmanageable toxicity. All patients registered adverse events of varying degrees, with 21 (63.6%) patients experiencing hyperglycemia (grade 3-4 – 30.3%) and 14 (42.4%) patients experiencing skin toxicity (grade 3-4 – 15.2%). In the SOLAR-1 study, the frequency of hyperglycemia was comparable (64.8%), and rash was noted in a third of all patients, which is comparable to our data. Conclusions: The results of using alpelisib with fulvestrant confirm its effectiveness in real-world clinical practice in patients with pre-treated HR+HER2- negative widespread breast cancer with the presence of somatic PIK3CA gene mutation. Brain involvement is an unfavorable prognostic factor in patients with PIK3CA mutation and increases the risk of death by 18 times, requiring the need to optimize the therapeutic algorithm, including through radiation methods. Discontinuation of the drug, which increases the risk of death by 8 times.