Recognizing invasive breast carcinoma of no special type with medullary pattern

Invasive breast carcinoma of no special type (IBC-NST) with medullary pattern is an uncommon histologic type of invasive breast carcinoma. It is associated with high-grade, poorly differentiated tumor cells that form large sheets of irregular confluent tumor cells associated with a prominent lymphocytic infiltrate. Patients with IBC-NST with medullary pattern are often postmenopausal women with a high body mass index and multiparity. We report the case of a 71-year-old woman who presented for routine screening mammography and breast mass suspicious for malignancy, initially thought to be invasive ductal carcinoma with an associated prominent lymphoid infiltrate. However, it was ultimately diagnosed as IBC-NST with medullary pattern, and radiologic imaging (particularly ultrasound and mammography) along with pathology review were critical in making the diagnosis. We make the case of the importance of radiographic imaging in diagnosing this condition, as the prognosis of IBC-NST with medullary pattern is typically more favorable compared to IBC-NST.