New insights into acinic cell carcinoma of the breast: clinicopathology, origin of histology, molecular features, prognosis, and treatment

Abstract

Acinic cell carcinoma (AciCC) of the breast is a rare malignant epithelial neoplasm, with approximately 60 cases reported in the literature. It predominantly affects women and exhibits significant histological heterogeneity. The diagnosis of breast AciCC is primarily based on the presence of eosinophilic and/or basophilic granular cytoplasm and markers of serous acinar differentiation. Despite being considered a low-grade variant of conventional triple-negative breast cancer (TNBC), over 25% of patients with breast AciCC have adverse clinical outcomes. Additionally, in early research, microglandular adenosis (MGA) and atypical MGA were considered potential precursors for various breast cancers, including intraductal carcinoma, invasive ductal carcinoma, adenoid cystic carcinoma, metaplastic carcinoma, and AciCC. Similarly, some studies have proposed that breast AciCC should be considered a type of carcinoma developing in MGA with acinic cell differentiation rather than a distinct entity. Therefore, the pathogenesis of breast AciCC has not yet been clarified. Moreover, to the best of our knowledge, the literature has not summarized the latest prognosis and treatment of breast AciCC. In this review, we synthesized the current literature and the latest developments, aiming at exploring the clinicopathology, histological origin, molecular features, prognosis, and treatment of breast AciCC from a novel perspective.

Keywords: acinic cell carcinoma; clinicopathology; immunohistochemistry; molecular genetics; salivary gland-type tumor; triple-negative breast cancer.

Figure 1

Histological characteristics of breast AciCC. Microscopically, the predominant morphologic patterns of breast AciCC are round to irregularly shaped acinars (A, H&E, ×200) and solid patterns (B, H&E, ×200). Both morphological structures usually merge together (C, H&E, ×200). Stromal tumor-infiltrating lymphocytes can be observed (D, H&E, ×200).

Figure 2

Immunohistochemical characteristics of breast AciCC. Breast AciCC is usually negative for ER (A, EnVision, ×200), PR, and HER2 and positive for LYS (B, EnVision, ×200), and S100 (C, EnVision, ×200). Because of the lack of peripheral myoepithelial cells, breast AciCC is negative for p63 (D, EnVision, ×200) and SMA (E, EnVision, ×200). Collagen Type IV (F, EnVision, ×200) staining shows the absence of basement membrane around glands and highlights the capillaries.