A Case of Rare Hormone-Sensitive Primary Adenoid Cystic Carcinoma of the Breast Diagnosed by Preoperative Core Needle Biopsy: A Case Report.

Adenoid cystic carcinoma (ACC) of the breast, a special histologic subtype of invasive carcinoma, most commonly originates in the salivary glands and is also found in the cervix, skin, bronchi, kidneys, esophagus, and prostate. ACC originating in the breast is quite rare, accounting for less than 0.1% of all breast cancers. Metastasis to lymph nodes or distant sites is very rare, and the "triple-negative" phenotype (negativity for hormone receptors and human epidermal growth factor receptor 2 [HER2]) is often noted. However, within the high prevalence of the triple-negative phenotype, hormone-sensitive primary ACC of the breast has been extremely rare, with few cases reported. The patient presented with pain around the right nipple persisting for several years. Mammography (MMG) and ultrasonography (US) revealed a mass in the right breast. Core needle biopsy (CNB) was performed. The results demonstrated that atypical cells proliferated invasively, exhibiting mesh-like, glandular, trabecular, and other structures. Formation of glands with eosinophilic discharge and pseudoglandular cavities due to retention of a mucinous edema-like matrix was observed, suggesting ACC. Skin-sparing mastectomy of the right breast and sentinel lymph node biopsy (SSM + SLNB) were performed with simultaneous breast reconstruction by implantation of tissue expanders. The results of surgical pathology were as follows: ACC, pT2 (5.0 cm × 3.8 cm × 2.3 cm), pN0 (sn 0/2), HG2, ly1, v1, estrogen receptor (ER) 20%, progesterone receptor (PgR) <1%, HER2 1+, MIB-1 index 15%.