Background: Breast cancer is the most frequent malignancy in women worldwide. Distinct intrinsic subtypes of breast cancer have different prognoses, and their relative prevalence varies significantly among ethnic groups. Hispanic/Latino (H/L) populations are a genetically admixed and heterogeneous group, with variable levels of European, Native American and African ancestries. Breast cancer in H/L patients is understudied from a molecular standpoint, and most studies reported so far include limited numbers of H/L patients and assign ethnicity based on self-reported data rather than ancestry. This is the first study to explore the prevalence of breast cancer intrinsic subtypes in Colombia and their association with clinicopathological data and genetic ancestry.

Methods: Immunohistochemistry surrogates from the 2013 St. Gallen International Expert Consensus were applied to classify breast cancer into intrinsic subtypes in 301 patients diagnosed between 2008 and 2012 at the Colombian National Cancer Institute. We analyzed the distribution of subtypes by age, histologic type, node status, margins at surgery, AJCC stage, tumor size, Bloom-Richardson grade, histologic features, administration and response to neoadjuvant therapy, adjuvant therapy and recurrence. Genetic ancestry was estimated from a panel of 80 ancestry-informative markers (AIM).

Results: Luminal B breast cancer subtype was the most prevalent in our population (47.5%), followed by luminal A (23.9%), non-basal triple negative (9.3%), basal-like (8.6%), HER2-enriched (8%), and unknown (2.6%). The average of age at diagnosis was 55 and the average tumor size was 4.08 cm. We found statistical significant differences in age at diagnosis, Bloom-Richardson grade, histologic features, adjuvant chemotherapy and recurrence according to intrinsic subtype. Consistent with North American and European observations, basal-like and non-basal triple negative were poorly differentiated tumors and more likely to be diagnosed at younger ages compared to luminal tumors. Patients diagnosed with HER2-enriched, basal and non-basal triple negative breast cancer had the highest African ancestry.

Conclusions: Luminal B tumors, a high risk subset of ER-positive breast cancer, occur with remarkably higher prevalence in Colombian women with breast cancer compared to North American and European populations. Triple-negative subtypes and HER2-enriched tumors appeared to be more frequent among patients with African ancestry, as observed in North American cohorts. Future studies analyzing the molecular profiles of breast cancer in Colombian women will help us understand the molecular basis of this subtype distribution and compare the molecular characteristics of the different intrinsic subtypes in Colombian Hispanic/Latina patients.

Citation Format: Serrano-Gomez SJ, Sanabria MC, Hernández-Suarez GA, Garcia O, Silva C, Romero A, Mejía JC, Fejerman L, Antonia T, Miele L, Zabaleta J. Increased prevalence of luminal B subtype in Colombian women with breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-08-09.