Synonyms

CMF

Category

Bone

Behaviour

Benign

Gender

Male

Tissue of Origin

Cartilage

Epidemiology

• Rare, <1% of primary Bone tumours
• Peak incidence 2nd–3rd decades
• Slight Male predominance
• Often misdiagnosed due to rarity and histological complexity

Clinical Features

• Pain and swelling, often mild and chronic
• May be asymptomatic - incidental finding
• Pathological fracture rare
• Soft tissue extension uncommon

Location

• Metaphysis of long Bones
• Proximal tibia most common
• Femur, fibula, foot Bones
• Flat Bones (pelvis, ribs) in older patients

Imaging

• Eccentric lytic lesion with lobulated scalloped margins
• Geographic Bone destruction with sclerotic rim
• May cause cortical expansion
• No mineralisation (unlike enchondroma/chondrosarcoma)

Pathology

• Lobular architecture with myxoid/chondroid matrix
• Cellular periphery, hypocellular centre of lobules
• Stellate and spindle cells
• GRM1 gene fusions (EWSR1-GRM1) detected in majority

Genetics

• GRM1 rearrangements (EWSR1-GRM1 most common)
• Unique molecular profile distinct from other cartilaginous tumours
• No IDH mutations

Treatment

• Curettage and Bone grafting - standard treatment
• En bloc resection for expendable Bones or recurrent lesions
• Local recurrence rate 15–25%

Prognosis

• Benign with Low recurrence rate
• Malignant transformation extremely rare
• Excellent long-term outcome after adequate surgery

Key Points

• EWSR1-GRM1 fusion gene is characteristic and diagnostically useful
• No IDH mutations - helpful to distinguish from Low-grade chondrosarcoma
• Histological misdiagnosis as chondrosarcoma not uncommon due to cellularity
• Curettage with adjuvants preferred to reduce recurrence

Workup - Blood Tests

No blood tests required

Workup - Local Imaging

• Plain radiograph
• CT - characterises lesion and cortical integrity
• MRI

Workup - Biopsy

• Biopsy if imaging atypical or diagnostic uncertainty
• Histology: nodular myxoid and chondroid areas with peripheral fibrosis

Workup - Staging

No staging required

Follow-up Summary

• Post-op visit at 6 weeks
• Year 1–2: 6-monthly clinical review + plain X-ray
• Year 3–5: Annual review with X-ray; discharge if no recurrence at 5 years
• No CT/MRI routinely required unless recurrence suspected on plain films
• No systemic metastatic risk - no chest imaging required
• High misdiagnosis rate: ensure final histology confirmed by sarcoma MDT before Follow-up plan