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4 slides generated from the cancer page, with a quiz from the open benchmark and speaker notes that cite the sources. Arrow keys move between slides; Print gives one slide per page.
Dedifferentiated chordoma is a rare form of chordoma in which part of the tumour has turned into a high-grade sarcoma, usually after recurrence or radiotherapy but sometimes from the start. The sarcoma part decides the outcome and made up 3 to 95 percent of the tumour in the defining series, smaller areas doing better, so it is treated with surgery and sarcoma chemotherapy.
The WHO bone classification lists dedifferentiated chordoma as a chordoma subtype defined by a high-grade sarcoma juxtaposed to conventional chordoma (Am J Surg Pathol 2020). In the ten-case series the tumours measured 2.8 to 24.5 cm (median 5.8), arose de novo or at recurrence including after radiotherapy in the sacrum (5), skull base (2), lumbar spine, mediastinum and as a lung metastasis, the dedifferentiated component made up 3 to 95 percent (median 60) and was pleomorphic to fibrosarcomatous, and by immunohistochemistry the conventional or chondroid component kept cytokeratin and brachyury while the dedifferentiated component lost both (Am J Surg Pathol 2020). The dedifferentiated component dictates survival, smaller areas carrying a better prognosis; it is more often diagnosed in recurrences and after radiotherapy but arises de novo in a few (JBJS British 2008).
How it differs from its parent: loss of brachyury in the sarcomatous part, rapid growth and early metastasis against the slow course of conventional chordoma, and a treatment plan that borrows from high-grade soft tissue sarcoma.
| Setting | Approach | Guideline |
|---|---|---|
| All cases | En bloc resection, radiotherapy as on the chordoma page, and anthracycline-based chemotherapy for the sarcomatous component; no trial in the subtype. | not mapped |