RESUMO
A 69-year-old male patient presented with a gradually enlarging mass in the left inner upper thigh for more than 2 months,and pigmented patches in the left medial leg for more than 20 years.Physical examination revealed a painless mass measuring 3 cm × 2 cm × 2 cm in size in the left inner upper thigh.Several pigmented patches were observed in the left medial leg,and the largest pigmented patch measured 2 cm× 2 cm in size with an irregular border and uneven pigmentation.The mass in the left inner upper thigh was resected and subjected to histopathological examination,which showed proliferative epithelioid neoplastic cells with mucous matrix,round and spindle cells of varying sizes separated by mucous matrix.The immunohistochemical study of tumor cells showed positive staining for vimentin,S100 and Melan-A,but negative staining for actin,desmin,CD56,epithelial membrane antigen,cytokeratin,leukocyte common antigen,CD99,chromogranin A and synaptophysin.Hematoxylin-eosin staining of pigmented patches on the left medial leg revealed squamous epithelium covering the surface of lesions with no superficial ulceration or atypia in epithelial cells,unevenly distributed melanophages,fibroplasia accompanied by collagen formation,obviously decreased skin appendages,infiltration of a few inflammatory cells in the dermis.AB-PAS staining was negative.The immunohistochemical study of pigmented patches showed positive staining for vimentin and Melan-A.The patient was pathologically diagnosed with metastatic myxoid melanoma with partial regression of the primary lesion.