Abstract

Chordomas are rare, malignant, osseous tumors with notochordal differentiation that affect the axial skeleton. Cutaneous metastasis is rare, and their characteristic immunohistochemical profile helps differentiate them from other tumors with similar histology. Conventional chordomas are positive for brachyury, pancytokeratin, EMA, and S100. They are usually negative for CK20. More recently, CDX2 was found not to be expressed in chordomas despite involvement in notochord regulation. This marker is normally expressed in cells of gastrointestinal origin. We describe a case of cutaneous metastatic chordoma with CK20 and CDX2 expression, as well as loss of S100. A 62-year-old female with history of sacral chordoma in 2010 status post resection with osseous and organ metastasis presented with a four-month history of an enlarging scalp lesion. Exam of the right parietal region showed a 3.5 x 3.0 cm pink to gray tumor. An excision was performed. Histologic sections revealed a proliferation of atypical epithelioid cells with clear cell features, vacuolation, and foci of eosinophilic cytoplasm, within a prominent myxoid matrix. Lesional cells were positive for brachyury, pancytokeratin, EMA, CK20, and CDX2. They were negative for S100, CK7, p63, CEA, desmin, SMA, and CD163. Abdominal imaging did not reveal any gastrointestinal masses. The histologic features, immunohistochemical profile, and patient history were most consistent with cutaneous metastatic chordoma. To our knowledge, this is the first report of chordoma with expression of CDX2. This unique immunohistochemical profile provides an unusual diagnostic challenge when differentiating between metastatic chordoma and other cutaneous tumors, particularly gastrointestinal metastasis. The expression of CK20 and CDX2 with loss of S100 could represent a biological mechanism of chordoma metastasis. More studies are needed to confirm this hypothesis.

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