Clear cell papillary neoplasm of the breast with MAML2 gene rearrangement: Clear cell hidradenoma or low-grade mucoepidermoid carcinoma?

Clear cell hidradenoma (CCH) is an uncommon adnexal tumor usually arising from eccrine glands and commonly seen on the face and the upper extremities. CCH occurring in the breast is extremely rare. Herein we report a case of MAML2-rearranged CCH of breast with a papillary architecture closely mimicking intraductal papilloma, adenomyoepithelioma and low-grade mucoepidermoid carcinoma, thus representing a source of diagnostic confusion. An overview of salient histologic features and immunophenotypes to distinguish CCH and low-grade mucoepidermoid carcinoma is also integrated into the report.