Abstract 5066: Molecular profiles of breast cancer in Barbados

Background: Breast cancer is a complex disease with varying incidence and mortality rates across populations. This study is the first investigation of molecular subtypes of breast tumors in a Barbados, West Indies population which is predominantly African in origin. Methods: To identify molecular subtypes of breast cancer we collected 260 formalin-fixed and paraffin-embedded (FFPE) tissue blocks from the Pathology Laboratory, Queen Elizabeth Hospital, St. Michael, Barbados. Pathologic features, including diagnosis, grade, tumor size, and axillary lymph node metastasis, were abstracted from pathology reports. Histology diagnosis, grading of invasive breast cancer and carcinoma in situ were performed using protocols of the College of American Pathologists and World Health Organization. Tissue microarrays were constructed from these 260 confirmed breast cancer samples and adjacent normal breast tissue at the University of Chicago. Immunohistochemical (IHC) assays were performed with commercial antibodies. To identify breast cancer subtypes, the tissues were evaluated for the expression of ER, PR, HER2, CK5/6 and EGFR. Vimentin staining served as a control for tissue fixation quality in archival tumors. Allred scores for ER and PR were calculated. HER2 was evaluated by IHC according to ASCO/CAP guidelines. EGFR was evaluated according to PharmDX recommendations. Vimentin and CK 5/6 were evaluated according to Dabbs, 2006. Breast cancer subtypes were defined as luminal A (ER+ and/or PR+, HER2-), luminal B (ER+ and/or PR+, HER2+), basal-like (ER-, PR-, HER2-, CK5/6+, and/or EGFR+), HER2+/ER- (HER2+, ER-, PR-), and unclassified (negative for all five markers). Results: The mean age of the breast cancer patients was 57 years old (SD=15 years). There were 63.7% patients with ER positive tumors, 50.6% with PR positive tumors, and 21.2% with HER2 positive tumors. The distribution of breast cancer subtypes was luminal A (52.5%), luminal B (12.7%), HER2+/ER- (8.5%), basal-like (24.6%), and unclassified (1.7%). The majority of patients had high grade tumors (52.3% grade II and 39.1% grade III). The luminal A and B tumors contained ductal and lobular types and several special types of breast carcinomas such as tubular, mucinous, cribriform, signet ring cells and acinic cell types. The basal-like tumors were more likely to be medullary carcinomas. The basal-like (70.2%) and HER2+/ER- (65.0%) tumors were more likely to be high-grade tumors than the luminal A (20.2%) and lu