Cystic hypersecretory ductal carcinoma of the breast: a rare cause of cystic breast mass.

We present the case of a surgically confirmed, invasive, cystic hypersecretory ductal carcinoma (CHDC) of the breast in a 43-year-old woman. The initial sonography showed a complex cyst, which required a core biopsy; however, the diagnosis was delayed as the patient refused to undergo the biopsy and the cyst decreased in size, as seen on follow-up sonography. Excision biopsy was performed, and invasive CHDC was diagnosed after regrowth of the cystic lesion. Meticulous sonographic evaluation of a cystic breast mass is always important, and pathology confirmation must be considered if the lesion shows features suspicious for malignancy, as a CHDC could be the cause of a cystic breast mass.