Microcystic adnexal carcinoma - aggressive infiltrative tumor often with innocent clinical appearance.

Microcystic adnexal carcinoma is a rare sweat gland malignancy, characterized by slow, but aggressive infiltrative growth. Histologic characteristics are follicular and glandular differentiation, as well as bland cytologic features. The benign histologic appearance, particularly in the upper level of the tumor, can be confused with syringoma or benign follicular neoplasm. Thus the risk of misdiagnosis is considerable, especially if only superficial biopsies are provided. We report two patients with microcystic adnexal carcinoma, using them as a basis to discuss, pathogenesis, diagnosis, histology and therapy of the tumor.