Synonyms

• Juvenile OS variant
• small cell OS

Category

Bone

Behaviour

Malignant

Grade

High

Gender

Both equally

Tissue of Origin

Bone

Epidemiology

• Rare small cell variant of osteosarcoma
• Similar age incidence to conventional OS
• Lower extremity predominance

Clinical Features

• Pain and swelling
• Rapid progression

Location

• Distal femur
• Proximal tibia
• Same sites as conventional OS

Imaging

• Radiograph: aggressive lytic/sclerotic lesion
• MRI: local staging
• CT chest: pulmonary staging

Pathology

• Small round cell sarcoma with focal osteoid production
• Can be misdiagnosed as Ewing sarcoma
• Osteoid is diagnostic feature

Genetics

• TP53, RB1 alterations
• Complex karyotype

Treatment

• MAP chemotherapy same as conventional OS
• Wide surgical resection
• Local control with surgery/radiotherapy

Prognosis

• Similar to conventional OS with modern chemotherapy
• 60-70% 5-year survival

Key Points

• Small cell variant but aggressive like conventional OS
• Osteoid production distinguishes from Ewing
• Treated identically to conventional OS

Workup - Blood Tests

• FBC, U&E, LFTs, Bone profile
• Alkaline phosphatase, LDH

Workup - Local Imaging

• Plain radiograph, MRI primary site
• CT chest, Bone scan/whole-body MRI

Workup - Biopsy

Core needle biopsy with osteoid identification critical

Workup - Staging

CT chest, skeletal staging