Adenoid Cystic Carcinoma of the Breast: A Case Report.

Adenoid cystic carcinomas (ACCs) are malignant tumors that most often occur in the salivary glands and bronchi, with occurrence in the breast being rare. ACCs of the breast reportedly give rise to few lymph node metastases or distant metastases and have a favorable prognosis. A 56-year-old woman with a left breast mass identified by mammographic screening was examined at our institute. Breast ultrasound revealed a sharply marginated, hypoechoic mass 12.7 × 9.4 × 8.7 mm in size in the upper outer quadrant of the left breast, and a vacuum-assisted biopsy (VAB) was performed at the mass site. Pathological examination of the VAB specimen revealed atypical cells with a cribriform growth pattern, and mucosal fluid surrounding tumor nests and within tumor ducts. The area around the tumor nests and inside of tumor ducts were also positively stained with alcian blue. These findings, we reached a pathological diagnosis of ACC. The preoperative diagnosis was stage I (cT1N0M0) triple-negative left breast cancer. Surgery consisted of breast-conserving surgery and sentinel node biopsy. The excised specimen was a 15.0 × 12.1 × 9.7 mm mass with a greyish white cut surface. Pathological examination of the excised specimen revealed a so-called adenoid cystic pattern. Results from immunohistochemical staining were identical to those from a VAB specimen, as they were estrogen receptor-negative, progesterone receptors-negative, and human epidermal growth factor receptor 2-negative, with low Ki67 expression. The final diagnosis, given the above findings, was left breast cancer (ACC) pT1N0M0 stage I triple-negative subtype.