Adenoid cystic carcinoma (ACC) is a rare subtype of invasive breast cancer, occurring in <0.1% of all malignant breast tumors. Though majority are triple-negative, ACC of the breast has good prognosis with a low incidence of regional and distant metastases.

A 45-year-old premenopausal female presented with a 5-month history of a gradually enlarging mass on her left breast. After core needle biopsy and subsequent metastatic work-up, she underwent total mastectomy with sentinel lymph node biopsy. Final histopathology showed adenoid cystic carcinoma, 2.1 cm in size and no lymph nodes positive for tumor. She has completed adjuvant radiotherapy of 50 Gy to the chestwall, and is currently well after 6 years of follow-up.

Surgery with either lumpectomy or mastectomy has been established as the mainstay of treatment of adenoid cystic carcinoma of the breast, but the use of adjuvant radiotherapy (RT) and chemotherapy has not been established. While adjuvant RT has been shown to improve cause-specific and overall survival following breast-conserving surgery, its indications after a mastectomy are not as well-defined. The decision to administer adjuvant RT was based on the current evidence indicating the advantages of adjuvant treatment for breast carcinomas, lack of survival difference between invasive ductal carcinomas and adenoid cystic carcinomas, indications for post-mastectomy RT in a retrospective Rare Cancer Network study, and reported incidences of local recurrences following mastectomy alone: 21.4% and 22.2%.

Our patient with adenoid cystic carcinoma of the breast, treated with surgery and adjuvant radiation therapy, showed favorable outcomes after 6 years.