Cutaneous PEComa, cutaneous clear cell myomelanocytic tumour

Primary cutaneous PEComa is a rare tumour comparable to PEComas found elsewhere.

Epidemiology

To date, twenty primary cutaneous PEComas have been reported. They are found across a wide age range with a female predominance2. There is no reported association with tuberous sclerosis.

Clinical features

The tumour presents as a painless slowly growing mass. Most cases occur on the limbs or limb girdles.

Histopathology

The tumour is located within the dermis, usually with infiltration of the subcutis which sometimes results in a dumbbell configuration. The tumour cells are nested; sometimes there is a focally trabecular architecture. The tumour cells may be purely epithelioid or a mix of epithelioid and spindle cells. The cells have clear or granular eosinophilic cytoplasm. Sometimes there are rhabdoid cytoplasmic inclusions. Cells may contain PAS-positive material2 . Multinucleate giant cells may be present. Mitoses are absent or scant and atypical mitoses are not seen. Thin-walled capillaries are prominent. Incorporation of surrounding collagen may cause a resemblance to benign fibrous histiocytoma.

Immunohistochemistry

	HMB45	10/101, 7/7(diffuse in 4 cases, focal in 3 cases)2
	Melan-A	5/71
	MiTF	5/51, 7/72
	NKIC3	6/62
	Melan-A	1/7(in one case, a few cells stained)2
	Desmin	5/101, 1/6(focal positivity in one case)2
	SMA	1/101, 1/72
	HHF35	0/62
	caldesmon	0/101
	calponin	0/101, 2/4(focal positivity in two cases)2
	S-100	1/101, 0/72
	MNF116	0/?101, 0/72
	EMA	0/?101
	AE1/AE3	0/21
	Cam5.2	0/31
	CD68	2/?101, 4/7(a few cells stained in 4 cases)2

Differential diagnosis

Balloon cell naevus.
Balloon / clear cell melanoma: shows a junctional component; strongly positive for S-100 but negative for desmin.
Dermal clear cell neoplasm: negative for melanocytic markers.
Clear cell benign fibrous histiocytoma: also occurs predominantly on the legs of women: show dermal hyperplasia with hyperpigmentation but rarely extend into subcutis: are negative for melanocytic markers HMB45 and MiTF but may show positivity for NKIC3.
Xanthoma, papular and eruptive: composed of xanthomatous cells: positive for CD68.
Atypical fibroxanthoma: occurs on the head of the elderly in sun-damaged skin: cells show atypia but are rarely of clear cell appearance.
Sebaceous carcinoma: positive for cytokeratins.
Metastatic renal cell carcinoma: positive for EMA, negative for melanocytic markers
Clear cell sarcoma of tendons and aponeuroses may extend into skin: positive for S-100 (and HMB45) but negative for muscle markers.

Prognosis

No recurrences have been reported after excision.

References

1 Liegl, Primary Cutaneous PEComa: Distinctive Clear Cell Lesions of Skin. Am J Surg Pathol 2008;32:608614

2 Mentzel T, Reisshauer S, Rutten A, et al. Cutaneous clear cell myomelanocytic tumour: a new member of the growing family of perivascular epithelioid cell tumours (PEComas). Clinicopathological and immunohistochemical analysis of seven cases. Histopathology 2005; 46:498-504

Crowson AN, Taylor JR, Magro CM. Cutaneous clear cell myomelanocytic tumor-perivascular epithelioid cell tumor: first reported case. Mod. Pathol. 2003; 16; 400A.