Abstract Background HER2-positive (HER2+) breast cancer (BC) accounts for 15–20% of all BC. Mutations in the PIK3CA gene are found in 25–30% of HER2 + BC cases and have been implicated in tumor progression and endocrine therapy resistance. Recent evidence suggests that a somatic PIK3CA mutation ( PIK3CA m) may serve as a marker of early progression in HER2 + metastatic BC. However, its precise prognostic significance across various lines of therapy and disease stages is not fully understood. We therefore aimed to evaluate the impact of PIK3CA m status on clinical outcomes in HER2 + BC patients. Methods We conducted a retrospective cohort study using data from the American Association for Cancer Research (AACR) Project GENIE Biopharma Collaborative (BPC). Overall survival (OS), Distant Recurrence-Free Survival (DRFS), and progression-free survival (PFS) were the primary outcomes. We compared patients with and without PIK3CA m and performed survival analysis using Kaplan-Meier methods and Cox proportional hazards models. Results We identified 212 HER2 + patients (150 early-stage and 62 Stage IV), of which 58 had a PIK3CA m. The median OS for the overall cohort was 125.1 months from treatment. Among early-stage patients, PIK3CA m was associated with a longer DRFS from diagnosis (37.7 months 95% CI 28.6–62.6 vs. 22 months 95% CI 16.8–32.8, p = 0.04). In contrast, among patients with Stage IV disease receiving first-line therapy, PIK3CA m was associated with a shorter median PFS (5.5 95% CI 1.6–32.2 vs. 14.9 months 95% CI 7.2–22.0, p = 0.04). PIK3CA m was not identified as an independent predictor of OS, DRFS, or PFS in univariable or multivariable regression analyses. Within the PIK3CA m subgroup, not having received hormone therapy was the only factor associated with worse survival on multivariable analysis (aHR = 4.51, 95% CI 1.77–11.5). Conclusion PIK3CA m was not found to be associated with worse OS, however it was associated with a shorter PFS among patients receiving first-line therapy, suggesting PIK3CA m could be explored as a predictive biomarker for identifying HER2 + Stage IV patients at higher risk of disease progression. These findings underscore the need for enhanced surveillance and personalized treatment strategies to manage disease progression in this patient subgroup.
Stabellini et al. (Sat,) studied this question.