Pulmonary tumor with notochordal differentiation: report of 2 cases suggestive of benign notochordal cell tumor of extraosseous origin.

Intraosseous benign notochordal cell tumor (BNCT) is a lesion postulated to be of notochordal cell origin. BNCT has recently been recognized as a potential precursor of classic chordoma, a rare malignant neoplasm usually presenting in the sacrococcygeal region, skull base, or mobile spine. Extra-axial chordoma is extremely rare, and only 2 cases of pulmonary chordoma have been reported previously. We describe herein 2 cases of hitherto-unreported lung tumors that were diagnosed as BNCT. The patients were a middle-aged asymptomatic man and woman who were each incidentally found to have a 15-mm pulmonary nodule on computed tomography. They underwent surgical resection of the tumors under a diagnosis of probable benign tumor of uncertain nature. Histopathologically, both tumors showed solid sheets of peculiar adipocyte-like univacuolated cells, multivacuolated cells, and less vacuolated cells with small, round nuclei and mildly eosinophilic cytoplasm. Mitosis was absent. These features were typical of BNCT. Immunohistochemically, the tumor cells in both cases were positive for brachyury, a transcription factor essential for notochordal cell differentiation and for other markers of notochordal cells including cytokeratins, vimentin, and S-100 protein. Postoperatively, extensive radiographic examination of the whole body revealed no evidence of a primary tumor elsewhere, and both patients are alive and well, with no evidence of disease 1 year after surgery. These 2 cases raise the possibility of a new explanation for the histogenesis of extra-axial chordomas: BNCT may be a precursor lesion of not only conventional axial chordoma but also of extra-axial chordoma.