Chordoma is a relatively rare malignant midline tumor arising in the axial skeleton, primarily at its cranial and caudal ends, that is derived from persistent embryonic notochordal cell rests. [1, 2, 3]
The notochord is derived from the primitive ectoderm and defines the midline of the chordate embryos. As the human fetus grows, the notochord expands at the site of the future intervertebral disks and forms the nucleus pulposus. The notochord regresses to leave an acellular sheath, except at its cephalic and caudal ends, where cell rests persist. Although this explains the observed distribution of chordomas (sphenoccipital and sacrococcygeal), it does not explain why the cell rests should transform into tumors.
A resemblance exists between notochordal and chordoma cells morphologically and immunohistochemically (positivity for S-100 protein, cytokeratin [CK], and epithelial membrane antigen [EMA]). [4, 5, 6]
Chordomas have been divided into the following three subtypes:
Chordoma represents 1-4% of all primary bone tumors in various series. The incidence of chordomas is reported to be 8.4 cases per 10 million population. These tumors occur mostly in adults, with an overall peak distribution in patients aged 55-65 years. Rare cases in children and older individuals have been described. Chondroid chordomas affect slightly younger individuals (mean age, 40 years). Males are affected twice as frequently as are females, with 30-50% of cases in the sacrococcygeal location.
The 5-year and 10-year survival rates for conventional chordoma are approximately 50% and 25-30%, respectively. Conversely, chondroid chordoma has 5-year and 10-year survival rates of approximately 80%. Survival rates appear to be influenced more by local tumor progression than by metastasis. [7, 8] A higher survival rate is associated with Hispanic race, smaller tumor size, and surgical intervention.
All three types of chordomas can metastasize, usually later in the course of the disease (except dedifferentiated chordomas, which can metastasize early). The usual metastatic sites are skin, bone, lung, and lymph nodes. Accurate prediction of metastatic potential is not possible, though certain clinical (local aggressiveness) and pathologic (anaplastic histology) features may be indicative. Vertebral body chordomas have a higher incidence of metastasis than do those arising in the clivus or sacrum. 
Some data suggest that female sex, tumor necrosis, and tumor volume of more than 70 mL are independent poor prognostic variables in skull-base chordomas. The difference in survival rate between the sexes suggests that hormone receptor status and hormone manipulation management may be areas for future investigation.