[Characterization of PIK3CA/AKT1/PTEN gene mutations in hormone receptor- positive/HER2-negative breast cancer]

Objective: To investigate the mutation of PIK3CA, AKT1 and PTEN genes in hormone receptor (HR)-positive and HER2-negative invasive breast cancer. Methods: A total of 44 formalin-fixed paraffin-embedded samples from HR-positive/HER2-negative female patients with breast cancer obtained between January 2020 and July 2024 in Peking Union Medical College Hospital were selected. The mutations of PIK3CA, AKT1 and PTEN genes were analyzed by next-generation sequencing (NGS), and the related clinicopathological characteristics were summarized. Results: In the cohort, 31 out of 44 cases (70.5%) exhibited alterations in the PIK3CA, AKT1 and PTEN genes. Of these, 83.9% (26/31) tumors harbored genetic abnormalities involving one gene, including 21 (47.7%, 21/44) PIK3CA, 2 (4.5%, 2/44) PTEN and 3 (6.8%, 3/44) AKT1 gene mutations. Mutations of both PIK3CA and PTEN genes were found in 16.1% (5/31) of specimens. Among the 26 cases with PIK3CA gene mutations, 13 variants were identified, including E542K, E545K, Q546K, H1047R, H1047L, G1049R, M1043I, C420R, P447_L455del, N345K, N345I, K711N and H1047L/V346G. In addition, 7 mutants of PTEN gene were determined (T319^*, T321Qfs^*23, Q245^*, Q171H, L108P, Y68Ifs^*6 and V343fs). For AKT1 gene mutation, only E17K was observed.Mutations of PIK3CA/AKT1/PTEN genes are more likely to occur over 40 year-old patients.In this cohort, the PIK3CA V346G mutation (co-existent PIK3CA H1047L) and the PTEN V343fs mutation were not found in previous publications. Conclusion: In addition to the predominance of common loci, PIK3CA and PTEN gene mutations also have rare loci mutations in the breast cancer, warranting further analysis with an expanded sample size.