Abstract: 【Abstract】 Objective To discuss the diagnosis and differential diagnosis of microcystic adnexal carcinoma （MAC）. Methods Totally, 10 patients with MAC were enrolled from Hospital for Skin Diseases, Chinese Academy of Medical Sciences from 2003 to 2017. Their clinical manifestations, histopathological and immunohistochemical features, treatment and prognosis were retrospectively analyzed. Results Of the 10 patients, 3 were males and 7 were females. Their average age at the onset of MAC was 51.65 years. Skin lesions all occurred on the face, and on the upper lip in 6 cases. The lesions usually presented as solitary plaque or nodule, and ulceration occurred in 4 cases. Histopathologically, skin lesions consisted of epithelial cords with different numbers of keratinous cysts and tubular structures, and neural involvement occurred in 6 cases. However, mitotic figures were rare. Immunohistochemical staining showed epithelial cells and keratinous cysts stained positive for cytokeratin, as well as tubular structures and glandular cavities stained positive for carcinoembryonic antigen and epithelial membrane antigen. All the patients received surgical excision, and one patient experienced in situ recurrence 13 years later. No distant metastasis occurred in these patients. Conclusions MAC mainly presents as red plaques with occasional ulceration on the upper lip. Its definite diagnosis depends on characteristic histopathological changes in bidirectional differentiation into hair follicles and sweat glands, and immunohistochemical features are helpful to distinguish MAC from other adnexal tumors.

Key words: Skin neoplasms, Pathology, clinical, Retrospective studies, Microcystic adnexal carcinoma