Malignant myopericytoma

Definition

A tumour showing the histological features of a myopericytoma along with malignant histological features.

Clinical features

These tumours may arise superficially or in deep locations in various anatomic sites. The patient may have a history of previous benign myopericytomas.

Macroscopic appearances

The tumours are poorly circumscribed.

Histopathology

There are myoid appearing oval or spindle cells with eosinophilic cytoplasm growing in a concentric perivascular pattern. Mitoses are frequent. There may be foci of necrosis.

Immunohistochemistry

	SMA	5/51
	Desmin	1/51
	AE1/AE3	1/51
	EMA	1/51
	S-100	0/51

Differential diagnosis

All of the below lack a concentric perivascular growth pattern.

Leiomyosarcoma: the cytoplasm is more brightly eosinophilic and the cells are plumper. They are usually positive for desmin but not in a dot-like pattern.
MPNST: there are typically alternating hypercellular and hypocellular areas. Nuclei are serpentine. 20% of cases show focal positivity for SMA and 50% are positive for S-100.
Monophasic synovial sarcoma: contain wiry collagen and cells do not appear myoid. At least focally positive for cytokeratins and EMA.

Prognosis

Four of five tumours pursued an aggressive course1.

References

1McMenamin, M. E. and C. D. Fletcher (2002). "Malignant myopericytoma: expanding the spectrum of tumours with myopericytic differentiation." Histopathology 41(5): 450-60.

This page last revised 12.1.2004.