Abstract: [Abstract] Objective To investigate the clinicopathologic characteristics of microcystic adnexal carcinoma (MAC) for improving the diagnosis. Methods One case of MAC was observed for its clinical symptoms, imaging features, analysising pathological characteristics and immunohistochemical phenotypes of surgical specimens, and also reviewed of relevant literatures. Results The main clinical manifestation of this old male patient was characterized by axillary mass with pain. Chest CT was showed the soft tissue image of a slightly lower density of the mass, and unevenly consolidated by the enhancement of the group. The pathological changes of tumor cells, cell clusters and adenoid structures, are significant. AE3 / AEI, CK19 and EMA positive staining of tumor cells ware demonstrated by immunohistochemistry. Conclusions MAC is a low-grade malignancy. The operation is not easy to be completely removed, and has higher recurrence rate. It is easy to be misdiagnosed for biopsy, and depends on surgical resection specimen to defininte diagnosis.

Key words: [Key words] Microcystic adnexal carcinoma, Diagnosis, Differential diagnosis