Chordoma: The Nonsarcoma Primary Bone Tumor

Chordomas are rare, slowly growing, locally aggressive neoplasms of bone that arise from embryonic remnants of the notochord. These tumors typically occur in the axial skeleton and have a proclivity for the spheno‐occipital region of the skull base and sacral regions. In adults, 50% of chordomas involve the sacrococcygeal region, 35% occur at the base of the skull near the spheno‐occipital area, and 15% are found in the vertebral column. Craniocervical chordomas most often involve the dorsum sella, clivus, and nasopharynx. Chordomas are divided into conventional, chondroid, and dedifferentiated types. Conventional chordomas are the most common. They are characterized by the absence of cartilaginous or additional mesenchymal components. Chondroid chordomas contain both chordomatous and chondromatous features, and have a predilection for the spheno‐occipital region of the skull base. This variant accounts for 5%–15% of all chordomas and up to 33% of cranial chordomas. Dedifferentiation or sarcomatous transformation occurs in 2%–8% of chordomas. This can develop at the onset of the disease or later. Aggressive initial therapy improves overall outcome. Patients who relapse locally have a poor prognosis but both radiation and surgery can be used as salvage therapy. Subtotal resection can result in a stable or improved status in as many as 50% of patients who relapse after primary therapy. Radiation therapy may also salvage some patients with local recurrence. One series reported a 2‐year actuarial local control rate of 33% for patients treated with proton beam irradiation.