Sclerosing rhabdomyosarcoma¹ (sclerosing pseudovascular rhabdomyosarcoma²)

Definition

This is a proposed rare subtype of rhabdomyosarcoma with an abundant matrix. It may represent a variant of embryonal rhabdomyosarcoma (evidenced by the presence of strap cells and the preferential expression of MyoD1 over myogenin).

Clinical features

The few cases reported occurred across a wide age range in adults and at a range of anatomical sites (forearm¹, hand¹ orbit¹, nasopharynx¹, jaw², lower leg², sacrum²), including sites unusual for other types of rhabdomyosarcoma.

Macroscopic appearances

These tumours are tan to yellow, rubbery and grossly infiltrative.

Histopathology

Margins are infiltrative. Coagulative necrosis may occur.

The tumour cells are spindled with varying amounts of eosinophilic cytoplasm. The cells have little cytoplasm and irregular nuclei with coarse chromatin and small nucleoli.

Abundant hyaline matrix resembles osteoid or chondroid, but lacks calcification or lacunae.

• Within the matrix, the neoplastic cells form small nests, lobules or trabeculae (as seen in sclerosing osteosarcoma or sclerosing epithelioid fibrosarcoma).

• Anastomosing chords may resemble angiosarcoma². Irregular spaces r lined by atypical cells forming small papillae and tufts.

• There may be a microalveolar pattern but not the large alveoli of alveolar rhabdomyosarcoma. The wreath-like giant cells of alveolar rhabdomyosarcoma are also lacking.

• Focally "strap cells" may be seen.

• The mitotic rate is typically high (> 25 mitoses per 20 HPF).

Immunohistochemistry

	Desmin	4/4, often limited, dot-like1, 3/3 (focal/weak in one case)2
	Myogenin	4/4, but limited1, 2/32
	MyoD1	4/4, diffuse1, 2/32, 2/3 (focal/weak in one case)2
	SMA	2/4, both diffuse1, 3/3 (weak/focal in one case)
	HHF-35	2/2, variable strength1, 3/3 (focal/weak in one case)2
	myf4	2/32
	Vimentin	2/22
	fast myosin	2/2 (focal/weak in one case)2
	Myoglobin	1/1 (focal/weak)2
	Pancytokeratin	0/22
	AE1/3	0/41
	EMA	0/12
	S-100	0/41, 0/22
	CD31	0/22
	CD34	0/22
	CD99	1/4 (strongly positive in one case)1, 0/22
	Collagen II	0/21
	Factor VIII	0/12
	NSE	0/12

Molecular genetics by PCR

	Pax3/FXHR fusion gene	0/11, 0/12
	PAX7/FXHR fusion gene	0/11, 0/12

Differential diagnosis

• sclerosing osteosarcoma: the matrix calcifies. Osteoclasts are present. The malignant osteoblasts commonly have an epithelioid morphology. Other patterns of osteosarcoma (chondroblastic, telangectatic) commonly co-exist.

• chondrosarcoma: the appearances are bland and there is a lack of highly malignant small round cells. There is true cartilage with lacunae. The vasculature has a branching pattern.

• alveolar rhabdomyosarcoma: patients are younger. There are well-formed pseudo-alveoli but they lack osteoid- or chondroid-like matrix and strap cells are very unusual. Staining for myogenin is almost always very strong. There is almost universally either a t(2;13)(q35;q14) translocation producing a Pax3/FXHR fusion gene, or a t(1;13)(q36;q14) producing a Pax7/FXHR fusion gene.

• leiomyosarcoma

• myofibroblastic sarcoma: also show stromal hyalinisation but the cytopalsm is paler and skeletal muscle markers are lacking.

• triton tumour (MPNST with rhabdomyoblastic differentiation)

• sclerosing epithelioid fibrosarcoma: there are foci of typical fibrosarcoma. Musclee markers are negative.

• angiosarcoma: the surrounding tissues are diffusely infiltrated by anastomosing vascular channels.

• PNET may show anomalous dot-like desmin positivity. Sclerosing rhabdomyosarcoma may also be CD99 positive.

• acantholytic / pseudovascular squamous cell carcinoma.

References

¹Folpe, A. L., J. K. McKenney, et al. (2002). "Sclerosing rhabdomyosarcoma in adults: report of four cases of a hyalinizing, matrix-rich variant of rhabdomyosarcoma that may be confused with osteosarcoma, chondrosarcoma, or angiosarcoma." Am J Surg Pathol 26(9): 1175-83.

²Mentzel, T. and D. Katenkamp (2000). "Sclerosing, pseudovascular rhabdomyosarcoma in adults. Clinicopathological and immunohistochemical analysis of three cases." Virchows Arch 436(4): 305-11.

This page last revised 26.12.2003.

©SMUHT/PW Bishop