Adenoid cystic carcinoma in situ of the breast: A case report

Adenoid cystic carcinoma (AdCC) is a rare entity in the breast. It is a biphasic malignancy with a slow-growing nature and a relatively favorable prognosis. While AdCC of the breast has been well characterized, adenoid cystic carcinoma in situ (AdCCIS) is barely reported in the literature. Our case involved a 40-year-old female patient who presented with a 2.5 cm mass in the left breast and was diagnosed of mammary AdCC. In addition, we identified three foci of AdCCIS containing glandular architecture and pseudoglandular spaces in terminal duct lobular units (TDLUs). Our case demonstrates the co-existence of AdCCIS and AdCC. However, it is not clear why it is rarely identified.