Correlates of Ki-67 proliferation index in a cohort of women with suspected breast cancer in Lusaka, Zambia

Ki-67 is a key biomarker of tumor proliferation in breast cancer, yet its clinical correlates in this population, where disease is often detected at earlier stages, remain underexplored. This study aimed to identify factors independently associated with high Ki-67 expression among women investigated for suspected breast cancer at Unilabs Laboratory, Lusaka, Zambia. A retrospective cross-sectional analysis was conducted on 208 women suspected of having breast cancer through a laboratory-based screening program in Lusaka, Zambia (2019-2024). Demographic, clinical, and pathology data were extracted from laboratory records. Ki-67 expression, as the outcome variable, was dichotomized as low (20%). Variables significant in bivariate analysis (p < 0.05) were included in a multivariable logistic regression model to identify correlates of high Ki-67 expression. The median age was 48 years (IQR: 40-63), and 46.2% (n = 96) exhibited high Ki-67 expression. In bivariate analysis, younger age, invasive ductal carcinoma, right breast involvement, progesterone receptor (PR) positivity threshold ≥10%, non-Quick Score scoring methods, and lack of fluorescence in situ hybridization (FISH) testing were associated with high Ki-67. However, in adjusted multivariable models, only older age (>41 years, aOR: 0.43-0.46, p < 0.05), PR positivity threshold ≥10% (aOR: 6.14-6.38, p < 0.05), and use of non-Quick Score scoring methods (aOR: 10.5-14.9, p ≤ 0.002) remained significantly associated with high Ki-67, while other factors lost statistical significance after controlling for confounders. In this diagnostic cohort from Zambia, nearly half of women with breast cancer exhibited high Ki-67 expression, reinforcing its relevance even in early detection settings. The study identified younger age (≤40 years), higher PR positivity threshold, and alternative scoring methods as independent correlates of high Ki-67, highlighting the importance of standardized biomarker assessment. Future studies should consider a prospective study design incorporating molecular subtyping to enhance the clinical interpretation of Ki-67 in similar populations.