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.