Breast Cancer Classification According to Immunohistochemistry Markers: Subtypes and Association With Clinicopathologic Variables in a Peruvian Hospital Database

Background: Molecular classification is an excellent prognostic and predictive method in breast cancer (BC). In this study. we evaluated differences in clinicopathologic features and overall survival (OS) in four BC molecular subtypes: luminal A, luminal B, basal cell-like, and HER2/neu. Patients and Methods: Immunohistochemical evaluation of estrogen receptor (ER), progesterone receptor (PgR), and HER2 was performed using a Peruvian hospital database of 1198 BC patients who were diagnosed between 2000 and 2002. Overall survival was calculated. Results: Out of 1198 patients with invasive BC, 49.3% were luminal A; 13.2%, luminal B; 21.3%, basal-like; and 16.2%, HER2. The mean of age at diagnosis was 51.5 years for luminal A; 49.6 for luminal B; 49.5 for basal-like; and 49.4 for HER2. The HER2 subtype showed 63.7% positive lymph nodes, 42.3% stage III and 9.7% stage IV cases. Basal subtypes showed the highest prevalence of a poorly differentiated phenotype (70.3%). Average follow-up was 60 months. Five-year OS was significantly different between all 4 groups (P<.0001); luminal A had the highest OS, followed by luminal B, basal-like; and HER2. Results are compared with other population studies. Conclusion: This study shows significant differences between the distribution of molecular subtypes and clinicopathologic features. Immunohistochemistry is useful in the clinical management of BC patients.