Answer

Nodular hidradenoma.

Discussion

Clear cell hidradenoma was first described in 1949; since then, it has been reported under various designations such as nodular hidradenoma and eccrine acrospiroma.^[1] Clinically, it presents as a slow growing, solitary firm nodule, mostly distributed over the scalp, face, thorax, abdomen, and gluteal region; mainly in adults. Some tumors discharge serous material while others have a tendency to ulcerate.^[1],[2]

The histopathological findings of nodular hidradenoma are classical. It is seen as a well circumscribed (often encapsulated) tumor containing an admixture of both solid and cystic components. The solid portion is composed of two types of cells, one cell type is polyhedral with a rounded nucleus and slightly basophilic cytoplasm; whereas the other cell type being round and having a clear cytoplasm due to the presence of glycogen. Nuclear grooving is found to be a useful morphological feature to aid in its diagnosis.^[1],[3] Squamous differentiation may be found, with infundibular type of keratinization being the most common type. Sebaceous differentiation is also common.^[4] Immunohistochemistry shows positive staining with antibodies against cytokeratin-CAM 5.2, Ber-EP4, p63, epithelial membrane antigen, S-100 protein, smooth muscle actin, and vimentin.^[2],[3],[4]

The tumor has a high rate of local recurrence (10%) and limited potential for malignant transformation. Malignant sweat gland adnexal tumors are rare with an incidence of 0.001%. Of these, clear cell hidradenocarcinoma accounts for 6% of malignant eccrine sweat gland tumors. Therapeutic options include surgical excision and Mohs micrographic surgery.^[5] The case is being reported for its rarity.

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Conflicts of interest

There are no conflicts of interest.