Rosette-forming epithelioid osteosarcoma

Clinical features

This unusual variant accounts for about 5% of all osteosarcomas. Most patients are in the second decade of life. There is a 2:1 male predominance. Lesions occur in the femur (n=13) and tibia (n=3).

Radiology

Similar to conventional osteosarcoma

Histopathology

All cases showed small nodules consisting of rosettes of cells surrounding stellate foci of osteoid. These nodules are bordered by blood vessels in a haemangiopericytomatous pattern. Six of 16 cases contained epithelioid osteoblasts.

Immunohistochemistry

rosette-forming epithelioid osteosarcoma conventional osteosarcoma of long bones EMA 10/16 5/10 NSE 8/16 8/10 CD56 14/16 6/10 CD99 3/16 0/10 Ki 67 index mean 47%, range 10% to 85% mean 50%, range 10% to 90% AE1/3 0/16 0/10 chromogranin 0/16 0/10 synaptophysin 0/16 0/10 neurofilament 0/16 0/10

Differential diagnosis

• Small cell osteosarcoma

• Primary or metastatic neural tumour: also NSE and CD56 positive

• Ewing's sarcoma / PNET: also CD99 positive

• Neuroblastomas: the rosettes are perivascular, not centred around osteoid.

• Metastatic carcinoma

Prognosis

Twelve of 16 patients died of disease, with an estimated 5 year survival of 15%. The outcome is poorer than for conventional osteosarcoma.

References

Okada, K., Hasegawa, T., Yokoyama, R. Rosette-forming epithelioid osteosarcoma: a histologic subtype with highly aggressive clinical behavior. Hum Pathol 2001;32:726-733

This page last revised 10.11.2001.