Clinical and pathological study on mixed tumors of the skin

Mixed tumor of the skin (MTS) is a rare benign tumor of the sweat glands with a reported frequency of 0.01% to 0.098%. The objective of the study is to investigate clinicopathological and immunohistochemical features of mixed tumor of the skin. This was a retrospective study of 21 patients diagnosed with MTS at the Institute of Dermatology and Venereology of Sichuan Provincial People's Hospital from 1980 to 2016. Pathological sections of all cases were reread and the diagnosis was verified. There were 14 males (67%) and 7 females (33%). MTS affected the face. The lesions were skin-colored or lightly red, with no subjective symptoms in most cases. Histopathologically, the tumors consisted of epithelial and interstitial components. The epithelium was mainly composed of cubic or polygonal cells, which can be seen within the tubule-like structures with bilayer epithelium. The inner cells mainly expressed cytokeratin and other epithelial markers. The outer cells expressed epithelial and mesenchymal markers. The outer cells expressed S-100, P63, and glial fibrillary acidic protein. The tumors showed interstitial mucus-like and fibrosis changes, and some parts had cartilage-like changes. Pathological diagnosis is particularly important because the clinical symptoms of MTS lack specificity.