Three Cases of Clear Cell Hidradenoma With "Benign" Lymph Node Involvement.

The malignant counterpart of cutaneous clear cell hidradenoma (CCH), hidradenocarcinoma, is an aggressive neoplasm that may have a fatal outcome. However, some cases of benign looking CCH with isolated lymph node involvement and excellent prognosis have been described. "CCH-like neoplasm of uncertain malignant potential" or "atypical hidradenoma" have been proposed as designations for these lesions. We report 3 cases of CCH with lymph node involvement. Ages ranged from 29 to 51 years old. All cases involved the inguinal lymph nodes: 2 of them presented with an isolated lymph node lesion, and the third case had lymph node and cutaneous involvement following the resection of a previous cutaneous lesion. Imaging studies showed no systemic involvement. None of the lesions exhibited histopathologic features of malignancy. All neoplasms were well circumscribed, had cystic spaces, did not display atypia or necrosis, and had less than 4 mitoses per high power field. No recurrence has been observed at follow-up after resection in all cases. All published cases of CCH with lymph node involvement so far affected a single lymph node in the axillary or inguinal regions, lacked features of malignancy, and had excellent long-term prognosis. Some cases previously reported as hidradenocarcinoma probably fit into this category. Our series adds more evidence to this rare phenomenon of "benign metastasis." Aggressive treatment should be avoided in these cases, and a long-term follow-up is warranted.