Adenoid Cystic Carcinoma of the Breast: A Rare Salivary Gland-Type Tumor with Favorable Prognosis

Adenoid cystic carcinoma (ACC) of the breast is an exceptionally rare malignancy, accounting for less than 0.1% of all breast cancers.Despite being a subtype of triple-negative breast carcinoma, ACC demonstrates a markedly favorable prognosis, with low rates of axillary lymph node involvement and distant metastasis.Histologically, the tumor is characterized by a dual cell population arranged in cribriform, tubular, or solid patterns.In this report, we present the case of a 65-year-old woman who detected a palpable mass in the upper outer quadrant of her left breast during self-examination.Imaging studies revealed a hypoechoic, spiculated lesion, which was subsequently classified as breast imaging-reporting and data system 4C.Core needle biopsy confirmed the diagnosis of ACC, with immunohistochemistry demonstrating estrogen receptor-negative, progesterone receptor-negative, human epidermal growth factor receptor2-negative status, and positive staining for (sex-determining region y)related high mobility group -box 10 and cluster of differentiation 117.The patient underwent breast-conserving surgery with sentinel lymph node biopsy, revealing negative nodal involvement.Histopathological examination confirmed ACC with 70% cribriform and 30% solid components, without perineural or lymphovascular invasion.Postoperative management included adjuvant radiotherapy (60 Gy) without chemotherapy.At 12 months post-treatment, no evidence of recurrence was observed.This case highlights the importance of accurate histological and immunohistochemical assessment in establishing the diagnosis and guiding treatment.Given its rarity and generally indolent course, awareness of ACC among clinicians and pathologists is essential to avoid overtreatment and to ensure appropriate surgical and radiotherapeutic management.