[Clinicopathologic characterization of malignant mixed tumor of the skin accompanied by eccrine porocarcinoma].

Objective: To investigate the clinicopathologic features, immunophenotype, pathological diagnosis and treatment of malignant mixed tumor (MMT). Methods: Clinical and pathological features including immunohistochemical phenotypes were analyzed in a case of MMT accompanied with eccrine porocarcinoma (EP) involving both hands, diagnosed definitely in January 2018 along with review of relevant literature. Results: A 64-year-old man presented with multiple rash on both hands for 4 years. Three lesions of 0.5 to 2.2 cm were removed for pathological evaluation. The pathological changes on little finger of left and right hands were MMT with EP, whereas that removed from the right ring finger was EP. MMT showed infiltrative growth with vascular wall invasion and consisted of epithelial (glandular or tube differentiation) and mesenchymal components (mucinous and/or cartilage stroma). The endothelial cells showed moderate to severe cytological atypia, nuclear pleomorphism and increased mitotic activity. The glandular component had histological characteristics of syringocarcinoma with moderately atypical chondrocytes but without myoepithelium. EP was composed of basal cells with visible vacuoles in cytoplasm and the presence of tubular and squamous differentiation, along with obvious atypia. Immunohistochemically cavosurface epithelium of glandular differentiation of MMT showed positivity for CK7, EMA and CD117. Myoepithelium showed S-100, CK5/6 and p63 positivity and stromal cells were positive for S-100. Differential diagnoses included metaplastic carcinoma, malignant myoepithelioma and atypical mixed tumor of skin. Conclusions: MMT with EP is extremely rare.The diagnosis of MMT depends on the morphologic features. Immunohistochemical staining is helpful for differential diagnosis. Surgical excision with safety margins is the treatment of choice. Complementary radiotherapy and/or chemotherapy is still controversial. The clinical course of MMT is deemed unpredictable and long-term follow-up is necessary.