Anaplastic sarcoma of the kidney

Definition

A proposed new rare renal sarcoma presenting predominantly in children, with a polyphenotypic mesenchymal pattern.

Epidemiology

Patients range from infants to forty years of age, most being children.

Clinical features

Patients present with a renal mass, sometimes with haematuria.

Radiology

Macroscopic appearances

The tumour is usually large (mean 13 cm). They appear soft, fleshy and friable. There is often a cystic component.

Histopathology

There is always a fascicular spindle cell component, sometimes showing a haemangiopericytomatous pattern. There are transitions to round/oval mesenchymal cells with a myxoid stroma. There are large pleomorphic multinucleate cells. Some cases include rhabdomyoblastic strap cells. Many cases include a a cartilaginous or chondroid component; less often there is an osteoid competent or osteoclast-like giant cells. Cysts are multilocular, with thin fibrous septa lined by hobnail cells. There is no epithelial component, although non-neoplastic epithelial elements may be entrapped and the epithelial cyst linings are thought to represent entrapped renal tubules.

Immunohistochemistry

	Vimentin	5/51
	Desmin	4/61
	MyoD1	0/51
	MYF4	1/4(focal weak nuclear positivity)1
	PGP9.5	4/51
	p53	3/61
	Cam5.2	0/31
	NB84a	0/41
	CD34	0/51
	CD56	1/61
	CD99	0/51
	WT1	0/61

Molecular studies

RT-PCR is negative for the SYT-SSX and ETV6-NTRK3 fusion transcripts.

Differential diagnosis

Anaplastic Wilm's tumour; includes blastemal and epithelial components, lacks extreme pleomorphism, lacks a cartilaginous component, positive for WT1 and CD56. 25% of cases contain nephrogenic rests.
Renal synovial sarcoma; lacks myogenous or cartilaginous differentiation, shows a SYT-SSX fusion transcript by PCR.
Malignant mesenchymoma also shows polyphenotypic mesenchymal differentiation but may represent a "waste basket" category.
Ectomesenchymoma; includes ganglion cells.
Mesenchymal chondrosarcoma: CD99 is positive but desmin is negative.
Biphasic sarcomatoid carcinoma of the renal pelvis with heterologous chondroid differentiation; has a malignant epithelial component.
Sarcomatoid renal cell carcinoma with divergent sarcomatoid growth pattern; has a malignant epithelial component.

Management

Surgery and/or chemotherapy have been used.

Prognosis

The initial evidence is that these tumour produce local recurrences, distal metastases and may be fatal.

References

1 Vujanic GM, Kelsey A, Perlman EJ, et al. Anaplastic sarcoma of the kidney: a clinicopathologic study of 20 cases of a new entity with polyphenotypic features. Am J Surg Pathol 2007; 31:1459-68

This page last revised 5.1.2008