Malignant melanoma with osteosarcomatous differentiation in a lymph node metastasis.

Osteocartilaginous differentiation in malignant melanoma is rare and can pose a diagnostic challenge. In previously reported cases, melanomas were predominantly located on acral and mucosal sites, with osteocartilaginous differentiation present in either primary or recurrent lesions. We report a case of a 52-year-old female with malignant melanoma located on the right upper back exhibiting osteosarcomatous differentiation only in the axillary lymph node metastasis. This case serves to highlight that the divergent differentiation can occur in lymph node metastases while being absent in the primary lesion. The patient's medical history, careful histological examination, and immunohistochemistry may be necessary for establishing the correct diagnosis.