PEComa of bone

PEComas presenting in bone may be primary or metastatic from extra-osseous sites.

Clinical features

Tumours occur across a wide adult age range. PEComas of bone most often involve the lower extremities. A significant proportion appear to be malignant.

Radiology

The tumour forms an osteolytic mass. There may be extension into adjacent soft tissue.

Histopathology

The tumour resembles that at other sites, being is composed of a combination of epithelioid and spindle cell with a nested pattern. There are delicate thin-walled capillaries which may be tightly surrounded by tumour cells.

Immunohistochemistry

	HMB45	5/61
	Melan-A	5/61
	SMA	6/61
	Desmin	3/61
	Caldesmon	1/31
	EMA	1/31
	TFE3	1/11
	Pan-K anticytokeratin	0/<61
	AE1/AE3	0/<61

Differential diagnosis

metastatic malignant melanoma: positive for S-100
metastatic carcinoma: positive for anti-cytokeratins
leiomyosarcoma: may be focally positive for HMB45.
Clear cell chondrosarcoma is less nested and usually contains numerous short trabeculae of woven bone.

References

1 Yamashita K, Fletcher CD. PEComa presenting in bone: clinicopathologic analysis of 6 cases and literature review. Am J Surg Pathol. 2010 ov;34(11):1622-9.