Osteosarcoma

Osteosarcoma, also known as osteogenic sarcoma, a malignant bone tumour.

General

• Most common malignant bone tumour in children.
• May be seen in the context of Li-Fraumeni syndrome.

Trivia:

• Terry Fox was afflicited by this tumour.

Definition

• Tumour that makes osteoid.
  • Osteoid = (extracellular) organic component of bone, normally produced by osteoblasts (cells which make bone matrix).

Gross

Classic locations:

• Distal femur ~ 45%.
• Proximal tibia ~ 20%.
• Proximal humerous ~ 15%.

Microscopic

Features:

• Cells with malignant features (e.g. nuclear membrane irregularities, marked nuclear size differences, mitoses) surrounded by delicate strands of osteoid.
  • Osteoid on H&E: pink, homogenous, "glassy".
  • Tumours typically very cellular - when compared to normal bone.
• Large (multinucleated) osteoclast-like giant cells may be seen.

Images

• 

  Osteosarcoma - intermed. mag. (WC)

• 

  Osteosarcoma - very high mag. (WC)

• 

  Small cell osteosarcoma - intermed. mag. (WC)

• 

  Small cell osteosarcoma - high mag. (WC)

www:

• Lace-like osteoid of osteosarcoma (nih.gov).

Subtypes

Subtypes:

• Conventional osteosarcoma (high grade).
  • Osteoblastic osteosarcoma.
  • Fibroblastic osteosarcoma.
  • Chondroblastic osteosarcoma.
• Small cell osteosarcoma.
• Telangiectatic osteosarcoma.
• Parosteal osteosarcoma.
• Periosteal osteosarcoma.
• Low-grade central osteosarcoma.
• High-grade surface osteosarcoma.
• Secondary osteosarcoma.
• Gnathic osteosarcoma - jaw bones - usually chondroblastic.

How to remember:

• Convention FOC = fibroblastic, osteogenic, chondroblastic.
• Low-grade central.
• High-grade surface.
• Parosteal.
• Periosteal.
• Small cell.
• Secondary.
• Telangiectatic.

Chondroblastic osteosarcoma

• Chondroid matrix present - may be prominent; osteoid may be a minor component.
• May be confused with chondrosarcoma.

Fibroblastic osteosarcoma

• Undifferentiated pleomorphic sarcoma-like/MFH-like.

Images:

• Fibroblastic osteosarcoma (upmc.edu).

Low-grade central osteosarcoma

• Well-formed bone.
• Usu. minimal nuclear atypia.

DDx:

• Fibrous dysplasia.

Telangiectatic osteosarcoma

• Rare.
• Extremely vascular.
• Prognosis similar to other types of osteosarcoma.

Important radiologic DDx:

• Aneurysmal bone cyst.

Parosteal osteosarcoma

• Arise from surface of bone.
• Low grade.
• Well-formed bone.

DDx:

• Fibrous dysplasia.^{[citation needed]}

Periosteal osteosarcoma

• Intermediate grade.

Small cell osteosarcoma

• May mimic (other) small round cell tumours.

Secondary osteosarcoma

Arises in the context of something else - causes:

• Paget disease of the bone (~80% of secondary osteosarcomas)
• Radiation (~15% of secondary osteosarcomas)).
• Prognosis often poor.

Images:

• Secondary osteosarcoma - several images (upmc.edu).

See also

• Chondro-osseous tumours.
• Bone.