To investigate the clinicopathological features, immunophenotype and differential diagnosis of clear cell hidradenoma, and to analyze the origin of clear cell hidradenoma and the underlying mechanism.

The clinical data of 23 cases of clear cell hidradenoma who underwent surgical resection in Suzhou Municipal Hospital between December 2017 and July 2021 were retrospectively analyzed. Clinical manifestation, imaging features, pathological features and prognosis of the 23 cases of clear cell hidradenoma were analyzed. Expression levels of epithelial membrane antigen, cytokeratin 20, cytokeratin 7, cytokeratin 14, carcinoembryonic antigen, and gross cystic disease fluid protein 15 were detected by immunohistochemical staining technique using the EnVision system. Periodic acid-Schiff (PAS) staining was performed to visualize glycogen.

Among the 23 cases, 8 were male and 14 were female, aged 14-94 years, with a median age of 55 years. The first symptom of clear cell hidradenoma was epidermal bulgels in 18 cases.Contrast ultrasonography showed a subcutaneous cystic solid echo mass with abundant blood flow in the solid part. The tumor histologically consisted of two types of cells: secretory epithelial cells or glandular epithelial cells and clear cells. Twenty cases had tumors with the features of benign clear cell hidradenoma. Two cases had atypical clear cell hidradenoma with atypia and mitosis. One case had malignant clear cell hidradenoma. Tumor cells were positive for epithelial membrane antigen, cytokeratin 7, cytokeratin 14, carcinoembryonic antigen, and gross cystic disease fluid protein 15 and they were Periodic acid-Schiff-positive. Twenty-three patients were followed up for 2-36 months, of which 4 were lost to follow-up and the rest had no recurrence of clear cell hidradenoma.

Clear cell hidradenoma is rare and has a good prognosis. Malignant clear cell hidradenoma is rarer and has a poor prognosis. Diagnosis of clear cell hidradenoma is mainly based on comprehensive analysis of pathological features and immunophenotypes. Clear cell hidradenoma should be differentiated from metastatic clear cell carcinoma, spiral adenoma, cortical adenoma, and malignant melanoma.

Adenoma, sweat gland; Skin; Adenocarcinoma,clear cell; Mucin-1; Keratinocytes; Pathology, clinical; Diagnosis, differential; Immunohistochemistry