Incidentally discovered distant cutaneous metastasis of sacral chordoma: a case with variation in S100 protein expression (compared to the primary tumor) and review of the literature.

Chordomas represent rare malignant primary bone tumors most often occurring in the sacral area. These tumors uncommonly involve the skin and often follow a progressive course with multiple recurrences, metastases and eventual death. Reports of cutaneous metastases from chordoma are very rare. The immunohistochemical staining characteristics of these cutaneous metastases with comparison to the primary tumors are similarly rarely addressed in the literature. We report a rare case of incidentally discovered, small, solitary distant cutaneous metastasis of sacral chordoma that developed on the right upper back of a 44-year-old man with a history of multiple completely excised melanomas who had also been previously diagnosed with chordoma involving the sacrum 12 years earlier. We describe its pathologic features with comparison to the primary tumor and briefly review the literature. Immunohistochemically, the cutaneous metastasis and primary tumor both stained positively for pancytokeratin and vimentin, as expected. However, the cutaneous metastasis unexpectedly lacked S100 protein expression, whereas the primary tumor was S100 positive. This phenomenon has only been documented in one other case report. We demonstrate that late, incidentally discovered cutaneous metastasis with unexpected immunohistochemical staining features rarely occur and can present a diagnostic challenge.