Abstract: Metastatic melanoma with osteo-cartilaginous differentiation is extremely rare and can be misdiagnosed as sarcoma. A 42-year-old male patient referred to clinic with left foot great toe onychomycosis for 3 years, nail plate stripping for 1 year, nail bed hyperplasia and blooding for half one year, had gone the debridement of the left foot hallux nail bed at Dec 2017. The patient was pathologically diagnosed with malignant melanoma, which was poorly treated by left foot hallux amputation, high-dose interferon and PD-1 immunotherapy, after multiple metastases, in which the inguinal nodule was pathologically diagnosed as metastatic malignant melanoma with osteo-cartilaginous differentiation, and then died.

Key words: melanoma, osteo-cartilaginous differentiation, pathological diagnosis