Chordoma is a malignant bone tumor of middle age-to-older adults found almost exclusively in the midline, most commonly in the sacrum (approximately half of all tumors) and base of skull. Symptoms are relatable to site of origin. Sacral tumors are more likely to be completely resectable. Local recurrences are not uncommon, and tumors are capable of metastasis to distant bone sites or lung. Subtypes include conventional chordoma, chondroid chordoma, and dedifferentiated chordoma (most aggressive).

These tumors produce osteolytic lesions on imaging and typically invade into surrounding soft tissue. Tumors cells are large and polygonal, and are often nested with a blue myxoid, bubbly stroma. Nuclei are medium-sized, round, and often have a small nucleolus. The abundant cytoplasm is eosinophilic and many tumors contain cells with characteristic large cytoplasmic vacuoles (‘physaliferous cells’). Mitotic figures and necrosis are uncommon. By immunohistochemistry the tumor cells are positive for AE1/AE3, CK8/18, S100, and brachyury. The differential diagnosis includes myxopapillary ependymoma (in spinal cord or nearby soft tissue; characteristic perivascular pseudorosettes, GFAP+ and S100+) and chondrosarcoma (S100+ but negative for keratins).