Breast cancer immunohistochemical patterns in Morocco: changes suggested by comparison with contemporary data

Background : Breast cancer remains a major public health challenge worldwide, with significant variability in tumor biology and outcomes. In low- and middle-income countries, immunohistochemistry (IHC) remains the cornerstone of tumor biological characterization due to limited access to genomic profiling. Understanding real-world IHC patterns is essential to contextualize prognosis and guide clinical decision-making in such settings. Methods : In this retrospective monocentric study, we described the immunohistochemical profile and surrogate molecular subtype distribution of breast cancer in a Moroccan cohort diagnosed in 2014 at a tertiary referral center in Casablanca. Results : Among 655 patients, IHC data were available for 456 cases and included estrogen receptor (ER), progesterone receptor (PR), HER2 status, and Ki-67 when reported. Estrogen receptor positivity was observed in 74.1% of cases with available data, and progesterone receptor positivity in 65.5%. HER2 positivity was present in 22.1% of tumors. Luminal A tumors accounted for 38.8% of cases, followed by luminal B (14.5%), HER2-positive (20.6%) and triple-negative tumors (13.9%), with a proportion of tumors unclassified due to incomplete data. Comparison with previously published Moroccan series suggests a temporal evolution in molecular subtype distributions, highlighting the influence of evolving IHC practices. Conclusions : These findings provide updated population-specific data on breast cancer immunohistochemical profiles and emphasize the continued relevance of IHC as a pragmatic tool in resource-constrained settings.