Chondrosarcoma
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Direct answer
Chondrosarcoma, a malignant cartilage-forming tumour of bone, is most common in middle-aged adults and favours the pelvis, proximal femur and ribs. Its radiograph shows lytic or lobulated destruction with popcorn or ring-and-arc calcification, and it is graded from I to III, with higher grades behaving more aggressively. Wide surgical resection is the mainstay of treatment, because the conventional types are largely resistant to chemotherapy and radiotherapy.
What you must remember
- Site: central sites such as the pelvis, proximal femur, proximal humerus, ribs and scapula, with the hands and feet rarely involved.
- Calcification: a popcorn or ring-and-arc pattern within a lytic lesion, reflecting calcified cartilage matrix.
- Malignant signs: endosteal scalloping, cortical destruction and a soft-tissue mass favour chondrosarcoma over enchondroma.
- Grading: grade I to III, based on cellularity, nuclear atypia and mitotic activity, with the grade predicting metastatic risk.
- Subtypes: clear cell chondrosarcoma in the epiphysis of young adults, and dedifferentiated forms, which behave aggressively.
- Molecular marker: IDH1 or IDH2 mutations are found in many cases and are relevant to classification.
- Treatment: wide surgical margins, with the mesenchymal subtype as the exception that responds to chemotherapy.
- Spread: the lung is the commonest site of metastasis.
Grade and subtype decide the treatment message
Chondrosarcoma is classified by histological grade and subtype, and each carries a different treatment message. Most conventional tumours are treated surgically whatever the grade, so the grades mainly guide prognosis. The table sets out the grades and the one subtype that responds to chemotherapy.
| Type | Cellularity and atypia | Metastatic risk | Treatment message |
|---|---|---|---|
| Grade I | Low cellularity, mild atypia | Low | Surgical excision with margins; limb-bone atypical cartilaginous tumours may be treated by extended curettage |
| Grade II | Moderate cellularity and atypia | Intermediate | Wide surgical resection |
| Grade III | High cellularity, marked pleomorphism | High | Wide resection, no proven systemic therapy |
| Mesenchymal | Small blue cells with cartilage islands | High | Surgery with chemotherapy |
Histological grade sets the prognosis, but the surgical margin decides whether the tumour recurs locally. Radiotherapy and chemotherapy are poor tools for the conventional types, so the surgeon does most of the work. Planning the margin on imaging before surgery is therefore the most important early step, and the biopsy tract must be placed so that it can be removed with the tumour.
Where the exam tries to catch you
The traps mostly involve expecting the wrong treatment or mistaking a chondrosarcoma for a harmless enchondroma.
- Trap: expecting chemotherapy to cure a conventional chondrosarcoma Correct: conventional chondrosarcoma is largely chemoresistant, so wide surgical excision is the cure.
- Trap: dismissing a large central pelvic popcorn lesion as an enchondroma Correct: enchondromas typically occur in the small bones of the hand and foot, whereas a large central lesion with endosteal scalloping suggests chondrosarcoma.
- Trap: treating mesenchymal chondrosarcoma like the conventional type Correct: the mesenchymal subtype responds to chemotherapy, so its plan must include systemic treatment.
Frequently asked questions
Where does chondrosarcoma usually arise?
Chondrosarcoma usually arises centrally in the pelvis, proximal femur, proximal humerus, ribs and scapula. The small bones of the hand and foot are rarely involved, which helps separate it from enchondroma.
Which chondrosarcoma subtype responds to chemotherapy?
Mesenchymal chondrosarcoma is the subtype that responds to chemotherapy, unlike the conventional types, which are largely resistant. It is an aggressive tumour that is usually treated with surgery combined with systemic therapy.
How is chondrosarcoma graded?
Chondrosarcoma is graded from I to III on cellularity, nuclear atypia and mitotic activity, and the grade predicts the risk of metastasis. Grade I is the least aggressive form and grade III the most aggressive.
What is the main treatment of conventional chondrosarcoma?
Wide surgical resection is the main treatment of conventional chondrosarcoma, because the tumour is largely resistant to chemotherapy and radiotherapy. Local recurrence is the main reason for failure, so margins are planned carefully on imaging.