The Role of Ki-67 in Predicting Breast Cancer Survival in Indonesia: A Prospective Cohort Study.

Background: Ki-67 is a widely used immunohistochemical proliferation marker with prognostic value in breast cancer, but its role in Indonesian clinical practice remains underexplored. This study aimed to evaluate the prognostic value of Ki-67 expression in predicting breast cancer overall survival among patients with invasive breast cancer treated at two hospitals in Central Java, Indonesia. Methods: A prospective observational study was conducted on patients with invasive breast cancer diagnosed at two hospitals in Surakarta, Central Java. Seventy patients with complete Ki-67, hormone receptor, HER2, and complete follow-up data were included. Ki-67 was categorized as positive or negative using a 20% cutoff. The primary outcomes were disease overall survival. Survival distributions were estimated using Kaplan-Meier curves and compared with log-rank, Breslow, and Tarone-Ware tests. Independent predictors were assessed with multivariable Cox regression adjusted for age, cancer stage, hormone receptor status, and HER2. Results: Of 70 patients, 41 (58.6%) had Ki-67 positive tumors, and 42 (60.0%) presented with stage III disease. Mean survival was shorter in Ki-67 positive versus negative tumors (61.1 vs 106.4 months; p = 0.030). In Cox regression, Ki-67 positivity independently predicted mortality (HR 3.07; 95% CI 1.19-7.92; p = 0.020), while advanced stage was also associated with higher risk of death (HR 3.20; 95% CI 1.08-9.43; p = 0.035). Conclusions: Ki-67 overexpression (≥20%) was significantly associated with worse overall survival and independently predicted mortality in this Indonesian cohort. Ki-67 may serve as a practical prognostic marker to support risk stratification in breast cancer patients.