Predictors of Survival Outcomes of HER2-Positive Breast Cancer Patients at a Tertiary Referral Hospital in Kenya

Background: HER2-positive breast cancer is an aggressive subtype associated with poor outcomes, particularly in low- and middle-income countries where access to targeted therapy is limited. Despite the growing burden of breast cancer in Kenya, comprehensive data on survival outcomes for HER2-positive patients remain scarce. Objectives: This study aimed to assess survival outcomes, including overall survival (OS), disease-free survival (DFS), and progression-free survival (PFS), among HER2-positive breast cancer patients treated at Moi Teaching and Referral Hospital (MTRH) in Kenya. Methods: This retrospective cohort study included 300 histologically confirmed HER2-positive breast cancer patients diagnosed between January 2018 and December 2023. Data were extracted from medical records, pathology reports, and treatment charts using a standardized abstraction tool. Kaplan-Meier methods were used to estimate survival outcomes. The log-rank test compared survival distributions between groups. Multivariable Cox proportional hazards regression identified independent predictors of survival. To address the substantial loss to follow-up (38.3%), sensitivity analyses including worst-case, best-case, and inverse probability of censoring weighting (IPCW) were conducted. Results: The 5-year overall survival was 82.3% (95% CI: 76.8–87.1%), with median OS not reached (lower bound 104.0 months). After IPCW adjustment, the 5-year OS estimate was 77.1% (95% CI: 70.4–83.8%). In unadjusted analyses, clinical stage (p=0.014) and metastasis status (p=0.040) were significantly associated with OS. However, in the multivariable Cox regression model, chemotherapy completion was the only statistically significant independent predictor of overall survival (HR=0.41, 95% CI: 0.19–0.89, p=0.024), adjusting for stage, metastasis status, trastuzumab completion, hormone receptor status, and age. Trastuzumab completion showed borderline significance for PFS (HR=0.37, 95% CI: 0.14–1.02, p=0.054). The 5-year DFS was 73.6% (95% CI: 66.8–81.2%). Conclusions: Survival outcomes for HER2-positive breast cancer patients at MTRH are favorable compared to historical regional data, though lower than high-income country benchmarks. Chemotherapy completion is associated with critical determinants of survival. Addressing financial barriers and improving treatment completion are essential to improve outcomes.