Osteosarcoma

Osteosarcoma
Diagnosis in short
Osteosarcoma. H&E stain.
LM	cells with malignant features (e.g. nuclear membrane irregularities, marked nuclear size differences, mitoses) surrounded by delicate strands of osteoid
Subtypes	conventional osteosarcoma (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
LM DDx	chondrosarcoma
Site	bone
Prevalence	uncommon
Clin. DDx	aneurysmal bone cyst,fibrous dysplasia, Ewing sarcoma

Osteosarcoma, also known as osteogenic sarcoma, a malignant bone tumour. It is grouped with the chondro-osseous tumours.

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 - low mag. (WC)

• 

  Osteosarcoma - intermed. mag. (WC)

• 

  Osteosarcoma - high 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.