Atypical Hidradenoma Mimicking Primary Mammary Carcinoma on Breast Fine-Needle Aspiration: A Case Report with Long-Term Follow-Up

Clear cell hidradenoma of the breast with MAML2 gene rearrangement

Clear cell hidradenoma is a rare benign tumor of the breast, its origin and pathogenesis are controversial. We have experienced a case of breast clear cell hidradenoma with mastermind like transcriptional coactivator 2 (MAML2) gene rearrangement. The patient found a painless mass with a hard texture in the left breast areola without nipple discharge. Microscopically, the tumor was cystic and solid, locally arranged in a glandular structure, covered by single cuboidal cells; it was composed of clear cells, epidermoid cells, and basaloid cells; there were no necrosis or mitotic figures. Immunohistochemical staining showed that the tumor cells positively expressed low-molecular cytokeratin 7, low-molecular cytokeratins (Cam5.2), high-molecular cytokeratin 5/6, cytokeratin 14, CD117, and p63; and did not express calponin, and smooth muscle myosin heavy chain. The cuboidal cells were positive for SOX10 but negative for p63. Additionally, periodic acid-Schiff reaction showed purple-red granules in the tumor cytoplasm, but Alcian blue staining showed no blue mucus in the cytoplasm. The split signals of MAML2 gene were detected by fluorescence in situ hybridization. Subtle histological and immunophenotypical differences may help to distinguish breast clear cell hidradenoma from common breast tumors. Furthermore, the MAML2 gene rearrangement may be a molecular genetic characteristic of breast clear cell hidradenoma.

Case Report and Literature Review of Nodular Hiradenoma, a Rare Adnexal Tumor That Mimics Breast Carcinoma, in a 20-Year-Old Woman

Nodular hidradenoma is an uncommon cutaneous adnexal tumor arising from sweat glands. In the skin, it usually presents as a solitary dermal nodule; excision is curative in most cases. In rare instances, it may present as a breast mass and can mimic breast carcinoma clinically and radiologically, causing diagnostic dilemmas for the treating physician and pathologist. Herein, we discuss a case of nodular hidradenoma in a 20-year-old Hispanic woman as a rapidly growing mass in the breast that mimicked breast carcinoma. We discuss the rare presentation of this uncommon tumor and the differential diagnosis of this entity, as well as the results of our literature review on the topic.