Breast cancer survival analysis in the Republic of Mauritius by age, stage at diagnosis and molecular subtype: A retrospective cohort study

Breast cancer is by far the leading cancer both in terms of incidence and mortality in the Republic of Mauritius, a Small Island Developing State (SIDS). However, few studies assessed its survival by age, stage at diagnosis and molecular subtype. We identified 1399 breast cancer cases newly diagnosed between 2017 and 2020 at the Central Health Laboratory, Victoria Hospital. Cancers were categorized into five molecular subtypes: (1) luminal A, (2) luminal B Her2 negative, (3) luminal B Her2 positive, (4) Her2 enriched and (5) Triple negative. The net 1 and 3-year survival were estimated for different age groups, staging at time of diagnosis and molecular subtype. We also estimated the excess hazards using a multivariate Cox proportional hazards model. While early stage at diagnosis (stage 1 [44.4%] and stage 2 [20.1%]) were most common compared to late presentation (Stage 3 [25.4%] and stage 4 [10.1%]), luminal B Her2 negative (36.7%) was the most frequent molecular subtype. The net 1- and 3-year breast cancer survival rates were 93.9% (92.3-95.4) and 83.4% (80.4-86.4), respectively. Breast cancer three-year survival rates were poorest among the youngest patients (<50 years), 77.1% (70.7-83.5), those diagnosed with stage 4 (28.5% [17.1-39.9]) and cancer with a triple negative molecular subtype (71.3% [63.3-79.3]). Emphasis on a national breast cancer screening programme, down staging breast cancer at diagnosis and systematic molecular subtyping of all breast tissues could be pivotal in improving breast cancer survival outcomes in the Republic of Mauritius.