Chordoma is a rare, slow growing, often fatal bone cancer derived from remnants of the embryonic notochord. It occurs mostly in the axial skeleton (skull base, vertebrae, sacrum and coccyx), is more frequent in males than females, and has a median age at diagnosis of 58.5 years, with a wide age range. This typically sporadic tumor is often advanced at presentation, and mortality is high due to local recurrence or distant metastases. The usual treatment is surgery, followed by adjuvant radiation therapy. Chemotherapy has not had a significant treatment role. Reports of a small number of families worldwide with two or more relatives with chordoma support a role for susceptibility genes in chordoma etiology. Recently we determined that duplications of the T gene co-segregated with disease in four multiplex chordoma families. The T gene encodes brachyury, a tissue-specific transcription factor that is expressed in notochord cells and is essential for formation and maintenance of the notochord. Some of the other chordoma families that we studied did not have T-gene duplications; the aggregation of chordomas in these families may result from changes in other susceptibility genes or other types of mutations targeting the T gene. We are continuing gene identification studies of multiplex chordoma families at the NIH Clinical Center under protocol 78-C-0039. We also want to determine whether alterations in any identified chordoma susceptibility genes are associated with sporadic chordoma in the general population.