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PH-MS08

Malignant bone, cartilage and joint tumours

Why metastases are the commonest malignant tumours in bone, how osteosarcoma, chondrosarcoma and Ewing sarcoma differ in age, site, genes and appearance, how they destroy bone and lift periosteum, and what lytic and sclerotic lesions cause.

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  • 5 steps · 10 questions
  • 3D normal anatomy

By the end, you can

  • Explain why metastases are the commonest malignant tumours in bone, and why myeloma, though it arises in marrow, is a haematological tumour.
  • Relate age and site within a bone to osteosarcoma, chondrosarcoma and Ewing sarcoma, with their key genetic changes.
  • Explain how an aggressive tumour destroys bone and lifts the periosteum to give a permeative margin, a Codman triangle, a sunburst or an onion-skin pattern.
  • Describe the gross and microscopic appearance of the main bone sarcomas and what grade and stage measure.
  • Contrast lytic and sclerotic metastases and relate bone destruction to pain, fracture, hypercalcaemia and spinal cord compression.
  • Recognise the classic gross, microscopic and radiological features, grades, stages and tests of malignant bone tumours, and explain how chemotherapy, surgery, radiotherapy and osteoclast inhibitors act on their mechanism.

What it is

Malignant tumours in bone are either primary, arising from bone, cartilage or other mesenchymal cells (osteosarcoma, chondrosarcoma, Ewing sarcoma and rarer types), or secondary: metastases from cancers elsewhere, which are far commoner. Myeloma, a plasma cell tumour of the marrow, is the commonest primary malignancy within bone but is classified with the haematological tumours. Primary malignant tumours of joints are very rare; synovial sarcoma, despite its name, does not arise from synovium.

5 types to tell apart
Bone-forming
Osteosarcoma: conventional (high grade, in the medulla), telangiectatic (blood-filled) and low-grade surface types such as parosteal osteosarcoma.
Cartilage-forming
Central chondrosarcoma (atypical cartilaginous tumour when grade 1 in a limb bone), secondary peripheral chondrosarcoma from an osteochondroma, and dedifferentiated chondrosarcoma.
Small round cell
Ewing sarcoma, defined by a fusion of EWSR1 (or rarely FUS) with an ETS family gene, most often FLI1.
Haematological tumours in bone
Myeloma and solitary plasmacytoma, and lymphoma of bone: tumours of marrow cells that destroy bone.
Metastases
Secondary carcinoma in bone, lytic (kidney, thyroid, lung), sclerotic (prostate) or mixed (breast).

US spelling: tumours → tumors, tumour → tumor, haematological → hematological.

Normal function

Bone remodelling, periosteum and red marrow

Bone is remodelled throughout life by two cell lines working together. Osteoblasts lay down osteoid, an unmineralised collagen matrix that then mineralises; osteoclasts, multinucleate cells fused from monocyte precursors, resorb bone when stromal cells and osteoblasts signal through RANKL. In adolescence most growth happens in the metaphysis, beside the growth plate, where cells divide fastest.

The shaft is a tube of compact bone built of . The covers it: a fibrous layer whose inner cells can form new bone, attached firmly to the cortex, so anything that lifts it provokes new bone. Inside, the spaces between the of spongy bone hold marrow.

In adults, blood-forming red marrow persists mainly in the vertebrae, pelvis, ribs, skull and the upper ends of the femur and humerus. Its wide sinusoids carry a large, slow blood flow, which matters for both myeloma and metastases.

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