Adenoid cystic carcinoma of the breast: A rare manifestation of a rare malignancy.

Adenoid cystic carcinoma (ACC) is a rare malignancy most commonly arising from the salivary glands. It less frequently manifests in other glandular tissues, including the breast, lacrimal glands, and the trachea. ACC is characterized by slow growth, yet exhibits locally aggressive behavior and propensity for late recurrence. Despite its local aggressiveness, the overall prognosis for primary breast manifestations of ACC is generally favorable. Mammographic and sonographic appearances often demonstrate an indistinctly marginated mass of variable shape and size. MRI findings are similarly variable, often demonstrating a lobulated or spiculated mass with variable patterns and kinetics of enhancement. As such, histopathological and immunohistochemical analysis are necessary for definitive diagnosis. In the breast, the mainstay treatment is lumpectomy or mastectomy with or without sentinel lymph node biopsy and post-operative radiation therapy. We present the case of a 61-year-old female patient with a high risk for breast malignancy who was found to have enhancing masses on a screening MRI of the breasts. Ultrasound-guided biopsy yielded a histopathological finding of ACC. Positive margins were identified on surgical pathology following lumpectomy and subsequent nipple-sparing mastectomy. This case demonstrates a rare exception to the tendency of radiographically smaller ACC masses to correlate with lower rates of disease persistence refractory to treatment, wherein a mammographically occult tumor with apparently limited disease on MRI produced multiple postsurgical finings of positive margins, necessitating multiple stages of excision and adjuvant radiotherapy.