Adenoid Cystic Carcinoma of the Breast in an Older Female: Diagnostic Pathway and Omission of Adjuvant Chemotherapy

Adenoid cystic carcinoma (ACC) of the breast is a rare special type of breast cancer that, although usually negative for hormone receptors and human epidermal growth factor receptor 2, typically follows an indolent course, in contrast with conventional triple-negative carcinomas.Its recognition may therefore change adjuvant treatment decisions.We report a case of a 72-year-old female with a slowly enlarging 1 cm lump at the junction of the upper quadrants of the right breast.Core needle biopsy showed an invasive carcinoma of histological grade 2 favoring ACC, negative for estrogen and progesterone receptors, with a human epidermal growth factor receptor 2 score of 0 and a Ki-67 index of 10%.Staging was negative.She underwent segmental resection with sentinel lymph node biopsy, which revealed a 1.1 cm grade 1 tumor without lymphovascular or perineural invasion, with free margins and a negative sentinel node.The diagnosis of classic ACC was based on morphology, with infiltrative cribriform and tubular nests forming pseudolumina, in the context of a triple-negative immunoprofile; ACC-supportive markers, such as myoepithelial markers and MYB, were not reported.Adjuvant chemotherapy, initially considered as for conventional triplenegative disease, was omitted, and she received adjuvant radiotherapy.Radiation dermatitis, an episode of delayed breast cellulitis, and persistent mild breast edema occurred, none of which required hospitalization.She remained free of disease 43 months after surgery.This case documents a pathway that is common in routine practice, in which classic ACC is diagnosed mainly on morphological grounds, and shows how recognition of this histological type led to the omission of chemotherapy.We discuss the differential diagnosis, the limitations of a diagnosis without ACC-supportive markers, and the retrospective evidence on axillary staging, radiotherapy, and systemic therapy.