Apocrine Breast Cancer: Unique Features of a Predominantly Triple-Negative Breast Cancer

Introduction Invasive apocrine carcinoma is a rare breast cancer that is frequently triple negative. Little is known about the characteristics of its molecular subtypes. We compared the incidence, demographics, and clinicopathologic features of this cancer with non-apocrine carcinomas stratified by molecular subtype. Methods Women with invasive apocrine cancer were retrospectively identified from the Surveillance, Epidemiology, and End Results (SEER) database. Clinicopathologic and demographic features were compared with non-apocrine carcinomas, both overall using data from 2004 to 2017 and stratified by molecular subtypes using data from 2010 to 2017. The life table method was used to determine the 7-year breast cancer-specific survival. Results Compared with non-apocrine cancers, apocrine cancers presented at a younger age, with larger, higher-grade tumors that were much more likely to be triple negative (50% vs. 11%) or human epidermal growth factor receptor 2 (HER2)-positive (28% vs. 15%) and less likely to be luminal (22% vs. 74%); however, the 7-year survival was the same at 85%. The characteristics varied dramatically by molecular type. Compared with non-apocrine triple-negative, apocrine triple-negative patients were less likely to be African American and were much older, with smaller, lower-grade tumors and much better survival (86% vs. 74%). In contrast, compared with luminal non-apocrine, apocrine luminal patients had larger, higher-grade tumors and worse survival (79% vs. 89%). Conclusions Invasive apocrine carcinomas have more aggressive features than non-apocrine carcinomas but the breast cancer-specific survival is the same. Half of these apocrine tumors are triple negative but these have more favorable features and much better survival than non-apocrine triple-negative cancers.