Malignant melanoma extending along the ulnar, median, and musculocutaneous nerves: a case report.

We analyzed a case of malignant melanoma that resembled malignant peripheral nerve sheath tumor with marked neurotropism. The subungual tumor in the right ring finger extended along the ulnar nerve for a distance of 30 cm, as well as along the median and musculocutaneous nerves, with lymph nodal metastases. The tumor consisted of interlacing spindle-shaped cells with large nuclei and distinct nucleolei. Immunohistochemically, the tumor cells were diffusely positive for S-100 protein. Five years after forequarter amputation, the patient is alive without disease. Malignant melanoma has the potential of invading several major peripheral nerves and must be distinguished from malignant peripheral nerve sheath tumor, which rarely metastasizes to regional lymph nodes.