Clinicopathologic features, treatment patterns and survival outcomes of acinic cell carcinoma of the breast: a national cancer database analysis

PURPOSE: Acinic cell carcinoma (ACC) of the breast is a rare malignancy characterized by serous acinar differentiation resembling salivary gland ACC. Although historically described as a triple-negative malignancy, its immunophenotypic profile and clinical behavior remain incompletely characterized. This study leverages a large national database to characterize the clinicopathologic features, treatment approaches, and survival outcomes of breast ACC.

METHODS: The National Cancer Database (NCDB) was queried for patients with invasive breast ACC diagnosed between 2004 and 2023. Overall survival (OS) was assessed using Kaplan-Meier analysis and compared with log-rank tests. Multivariable Cox regression analysis was used to evaluate independent associations with OS.

RESULTS: A total of 149 patients with breast ACC were identified. Mean age was 57.8 ± 14.3 years, and median tumor size was 2.0 cm. Most patients presented with early-stage disease (Stage I-II, 86.7%). 44.6% demonstrated poorly differentiated or anaplastic tumors. Node-positive disease was present in 27.0% of patients. Hormone receptor expression was common (ER 57.1%, PR 50.7%), while 93.5% were HER2-negative. The 5-year OS was 82.9%. Older age (p < 0.001), advanced stage (p < 0.001), and nodal positivity (p = 0.038) were associated with worse OS. Surgical resection was associated with improved survival (p < 0.001), while radiation, chemotherapy and hormonal therapy were not associated with OS. On multivariable analysis, surgical resection remained independently associated with survival (HR 0.03, 95% CI 0.005-0.25, p < 0.001).

CONCLUSIONS: Breast ACC presents at an early stage with hormone receptor heterogeneity. Surgical resection was the only modality independently associated with improved survival.