Understanding international genomic diversity for breast cancer: Comparison of molecular subtypes of breast cancer in very young women (age ≤ 35) between Izmir (Western Turkey) and Boston (Massachusetts, USA).

Abstract

e12509 Background: One in forty women is diagnosed with breast cancer at a very young age (≤35 years). Studies suggest breast cancer molecular subtypes are different in young women, with a higher prevalence of triple negative and HER-2+ disease. Objective: Explore the impact of genetic diversity on molecular subtyping of very young breast cancer patients in geographically and ethnically diverse populations: Turkey and the United States. Methods: A retrospective analysis of women ≤35 years of age diagnosed with breast cancer from 1999-2011 at Ege University Faculty of Medicine (EUFM) and Boston Medical Center (BMC). Data were collected and abstracted from hospital cancer registries and electronic medical records. Molecular subtyping was based on immunohistochemical evaluation of estrogen, progesterone receptors, Ki-67, and HER2/neu. Bivariate analysis was conducted using Chi-Square and Fisher’s Exact tests. Results: There were 206 and 45 patients from EUFM and BMC, respectively. Mean age at diagnosis was 31.4±3; most were white (87%), parous (70%), had breast fed (74%), and no1st degree relatives with breast cancer (92%). BMC patients were younger (31.7±3 v. 29.9±3 p=.0006) and more racially diverse (0% v. 60% black/hispanic p <.0001). There were clinicopathological differences between EUFM and BMC, including: histological subtype (IDC 68% v. 93% p=.02), HER-2/neu positivity (60% v. 16% p <.0001), and Ki67 ≥15% (54% v. 83% p=.008). Missing data precluded subtyping in 25% and 22% of women at EUFM and BMC. Of subtypes determined, prevalence was the same; however, EUFM had more Luminal B and less Triple negative patients then BMC. Conclusions: Population-level similarities and proportional distinctions exist in molecular subtypes of breast cancer for women ≤35 years. In both countries, Luminal B and triple negative sybtypes were most common suggesting younger age rather than genetic diversity is an important determinant of molecular subtyping. [Table: see text]