Prognostic Value of Phosphatidylinositol-3 Kinase p110 α Protein Expression in Patients with Stage I–III Invasive Breast Cancer

Background: The prognostic value of phosphatidylinositol-3-kinase p110α, a key catalytic subunit in the PI3K/AKT pathway, in breast cancer remains controversial. This study evaluated its prognostic significance in stage I–III invasive breast cancer. Methods: p110α protein expression was detected via immunohistochemistry (IHC) in 161 patient tissue samples. Its association with overall survival (OS) and relapse-free survival (RFS) was analyzed using Kaplan–Meier and Cox proportional hazards models. Results: p110α positivity was detected in 59.0% of specimens and showed significant correlation with histological grade (p = 0.034). Survival analysis revealed that p110α positivity was associated with worse OS (log-rank p = 0.008) and RFS (log-rank p = 0.018). In multivariate analysis, p110α expression was an independent predictor of poor prognosis for both OS (HR = 2.45, 95%CI: 1.25–4.78) and RFS (HR = 2.12, 95%CI: 1.14–3.94). This association with poor prognosis was particularly pronounced in stage I–II, hormone receptor (HR)-positive, and human epidermal growth factor receptor 2 (HER2)-negative subgroups. Supporting evidence from the PROGgeneV2 database showed that high PIK3CA mRNA levels predicted inferior survival in external cohorts. Conclusions: p110α protein expression is an independent biomarker for adverse outcomes in stage I–III invasive breast cancer. Its assessment could improve prognostic evaluation and guide personalized therapy.