Prevalence of somatic PIK3CA mutations in hormone receptor-positive metastatic breast cancer: The Indian experience.

e13047 Background: The phosphatidylinositol 3-kinase (PI3K) inhibitors have been found to improve survival outcomes in hormone receptor-positive metastatic breast cancer (MBC) and are FDA-approved in this setting after progression on hormonal therapy. However, real-world data from India on the prevalence of PIK3CA mutations is scarce. Methods: This is a retrospective study including patients with hormone receptor-positive breast cancer registered at our center between January 2017- and December 2023 who developed metastatic disease on follow-up after getting appropriate treatment (adjuvant /neoadjuvant) as per institutional protocol. The PIK3CA mutation testing was done on the biopsy specimen. FDA-approved therascreen PIL3CA RGQ PCR kit from Qiagen was used and the assay is a real-time qualitative PCR test for the detection of 11 mutations phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) gene (Exon 7: C420R; Exon 9: E542K, E545A, E545D 1635G>T only, E545G, E545K, Q546E, Q546R; and Exon 20: H1047L, H1047R, H1047Y) using genomic DNA (gDNA) extracted from formalin-fixed, paraffin-embedded (FFPE) breast tumor tissue. The clinical demographics of patients with PIK3CA mutations were extracted from the hospital database and represented descriptively. Results: A total of 80 consecutive patients with hormone-positive breast cancer at relapse were screened and 26 were found to have PIK3CA mutations (32.5%) of which 24 were female (92.3%). The median age of patients with mutated PIK3CA cases was 50 years (range: 31 to 72 years). The clinical stage of disease at presentation was: stage II in 11.5%, IIIA in 23.1%, and IIIB in 65.4% of cases. The median time of relapse was 21 months from diagnosis (range: 10 to 42 months). The disease sites at relapse were multiple in 23 patients (88.46%) [including central nervous system (CNS) relapse in 3 patients) and CNS (brain) only in 3 patients (11.54%). The mutations detected included H1047R (3140A>G at exon 20) in 8 cases, E545K (1633 G>A at exon 9) in 5 cases, Q546R (1637 A>G at exon 9) in 4 cases, E542K (1624 G>A at exon7) in 3 cases and synchronous mutations (E542K/E545K at Exon 7) in 3 cases and (H1047R/H1047L at exon 20 ) in 3 cases. Only eight patients received alpelisib with fulvestrant due to financial constraints. Conclusions: This is the first Indian study that describes the prevalence of PIK3CA mutations in hormone-positive breast cancer at relapse. Around one-third of patients harbor this mutation and 23.1% of cases have CNS involvement at relapse. The most common PIK3CA mutation detected was H1047R (exon 20) followed by E545K (exon 9).