Characterization of breast cancer molecular subtypes, clinicopathological features and survival outcomes in Rwandan women: a retrospective cohort study

Breast cancer (BC) remains a leading cause of cancer-related morbidity and mortality worldwide, with substantial disparities in incidence, subtype distribution, and outcomes across different populations and settings. In Rwanda, evidence regarding the molecular subtypes of BC and their associations with sociodemographic, clinical and pathological characteristics remains limited. We conducted a retrospective cohort study of women with histologically confirmed BC between January 2014 and June 2021 across four major referral hospitals in Rwanda. Data on sociodemographic, clinical, and pathological characteristics—including ER, PR, and HER2 immunohistochemical status—were extracted from medical records. Tumors were categorized into Luminal A/B (ER + and/or PR+), HER2-enriched (ER-/PR-/HER2+), and triple-negative breast cancer (TNBC; ER-/PR-/HER2-). Associations between subtype and key features were assessed using chi-square and Fisher’s Exact tests and multinomial logistic regression. Survival analysis was performed using the Kaplan-Meier method. The mean age (± SD) among women ( N = 889) included in this analysis was 50.9 (± 12.9). The most common molecular subtype was luminal A/B (67%), followed by HER2 enriched (18.2%) and TNBC (14.8%). The distribution of molecular subtypes varied significantly by tumor side ( p = 0.01), stage at diagnosis ( p = 0.006), imaging modality used ( p = 0.003), and receipt of hormonal therapy ( p < 0.001). Histologic grade showed a statistically significant association with molecular subtype distribution ( p < 0.001) with Grade I and II tumors having high proportions of Luminal A/B (76.5% and 74.6%, respectively), while grade III tumors had a markedly lower Luminal A/B percentage (56.9%) and higher proportions of HER2-enriched (21.1%) and TNBC (22.0%) subtypes. After adjustment, TNBC were more likely to be of grade III histology with an aOR of 3.8 (95% CI, 1.6–8.9). Five-year overall survival was 43%. Among Rwandan breast cancer patients, Luminal subtype was most common, followed by HER2-enriched and TNBC. Molecular subtype distribution varied by histologic grade and stage at diagnosis, while grade III histology was associated with TNBC after adjustment. The 5-year overall survival was low at 43%. These findings highlight the urgent need for early detection, expanded molecular testing, and equitable access to specialized care.