Nodular hidradenoma of the breast: report of two cases with literature review.

Two cases of nodular hidradenoma of the breast with possibly different origins are reported. Case 1 is of a 58-year-old female with a breast mass in the left, outer lower-quadrant. A histogenetical origin in the skin adnexal glands was suspected due to its superficial location and immunohistochemical findings. Case 2 is of a 44-year-old male with a subareolar nodule and nipple discharge. Histological examination demonstrated that the tumor was located deep in the breast tissue, was surrounded by dilated mammary ducts and exhibited intraductal extensions, which are all features mimicking those of breast cancer. Immunohistochemical positivity against gross cystic disease fluid protein-15 was weakly identified and negativity for endoplasmic reticulum was observed. This case can be interpreted as arising in the mammary ducts. It is well known that various kinds of skin adnexal tumors arise in the breast tissue; however, nodular hidradenoma of the breast is still a rare benign neoplasm. Clinically, nodular hidradenoma of the breast tends to occur in the nipple or subareolar region of the female breast. It should be kept in mind that nodular hidradenoma may occur in mammary ducts and it should be included when differential diagnoses are made of subareolar breast tumors.