11P - The prognosis of rare histopathologic subtype of breast cancer

Abstract

BackgroundBreast cancer is a heterogeneous disease with various histopathologic subtypes. As the prevalence of special types of breast cancer other than invasive carcinoma of no special type (NST) is low, limited data about the clinical behavior and prognosis according to the histologic types were documented with discordant results. The purpose of this study was to analyze the characteristics and the prognosis of rare histopathologic subtype of breast cancer compared with NST and to understand better for proper management. MethodsA total of 133,969 patients were analyzed in this study among the patients who were registered in the Korean Breast Cancer Society Registry database between January 1996 and March 2019 in Korea. ResultsThe prevalence of special types of breast cancer other than NST was 13.7% (n = 18,633). The patients with lobular, mucinous, tubular, papillary, and cribriform carcinoma presented as luminal A subtype much more than NST (77.6%, 74.6%, 77.2%, 57.4%, and 78.1% vs 47.5%, respectively, p < 0.001). A micropapillary carcinoma included more luminal B subtype with even high K-67 expression or positive HER2 than NST (40.9% vs 29.5%, p < 0.001). Typically, medullary and metaplastic carcinoma included more triple negative breast cancer (44.8% and 64.8% vs 13.5%, p < 0.001) than NST. In survival analysis, lobular (HR 0.879, p = 0.029), mucinous (HR 0.529, p < 0.001), tubular (HR 0.781, p < 0.001), papillary (HR 0.728, p < 0.001), medullary (HR 0.500, p < 0.001), and cribriform carcinoma (HR 0.291, p = 0.001) showed better overall survival than NST, and metaplastic carcinoma (HR 1.995, p < 0.001) showed worse outcome significantly. However, after adjusting for age, stage, molecular subtypes, grade, and lymphovascular invasion, only metaplastic carcinoma showed different overall (HR 1.762, p < 0.001) and breast cancer-specific survival (HR 1.685, p = 0.012) from NST. ConclusionsIn conclusion, invasive breast cancer had specific clinical and pathologic features according to the histopathologic subtype. However, special types of breast cancer other than NST have similar survival outcomes compared to NST when adjusting for other prognostic factors, except for metaplastic carcinoma. Editorial acknowledgementThis research was supported by the Korean Breast Cancer Society. Legal entity responsible for the studyThe authors. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.