Acinic Cell Carcinoma of The Breast: A Population-Based Clinicopathologic Study

Abstract

Purpose Acinic cell carcinoma (ACC) of the breast is a very rare, primary salivary gland-type breast malignancy with ~ 100 reported cases in the literature. Limited information about the clinical features and outcomes of the patients with ACC is available. Methods We utilized the Surveillance, Epidemiology, and End Results (SEER) database to identify ACC cases diagnosed between 2000 and 2018. For comparison, we also examined a cohort of invasive breast carcinomas of no special type (NST). Results Thirty ACC cases were identified among over 248,000 invasive breast carcinoma NST cases in the SEER database. Most ACC cases affected the White population (87%) and individuals over 50 years old (70%). ACCs were predominantly grade 3 carcinomas (44%), diagnosed at an early stage (AJCC TNM stages I and II, 67%). Hormone receptor (HR) and HER2 status were available for 13 cases, revealing molecular heterogeneity: HR-/HER2- (four cases, 31%), HR-/HER2+ (two cases, 15%), HR+/HER2- (four cases, 31%), and HR+/HER2+ (three cases, 23%). Surgery was the primary treatment modality for 26 out of 30 (86.7%) ACC patients, with chemotherapy and radiotherapy used in 46.7% and 33% of cases, respectively. The median survival time for ACC patients was 19 months compared to 48 months for invasive breast carcinoma NST patients (p < 0.001). Year-wise survival rates for ACC patients showed a dramatic decrease in the number of at-risk patients over time, starting at 30 months and decreasing rapidly, compared to a slower decline in the invasive breast carcinoma NST group (p < 0.01). The log odds of death for ACC patients were significantly higher (by 4.5 times) than for invasive breast carcinoma NST patients (p < 0.01), indicating a substantially worse prognosis. Conclusions Acinic cell carcinoma of the breast is a very rare (0.01%) primary breast malignancy. Despite its early clinical presentation, ACC of the breast appears to have a more aggressive clinical course and poorer clinical outcomes compared with conventional breast cancer.