i) Desmoplastic Small Round Cell Tumour

Epidemiology

Desmoplastic Small Round Cell Tumour (DSRCT) is a rare soft tissue sarcoma that usually affects children, adolescents and young adults; the median age of diagnosis is the third decade of life. Men are much more commonly affected (90% of cases).

Aetiology and Pathogenesis

Exact aetiology is unknown. Translocation of chromosomes 11 and 22 is a universal feature and the aetiology is likely related to this.

Clinical Features

Most patients present with abdominal disease, often with multifocal involvement of the retroperitoneum, omentum and mesentry; there are often many serosal deposits. Other mesothelial surfaces may be involved, including pleura and the tunica vaginalis of the scrotum, but these are exceptionally rare.
Symptoms include abdominal pain, bloating, and weight loss. Patients may present with symptoms relating to obstruction of the gastrointestinal tract, ureters or hepatobiliary system. Signs depend on the extent of involvement; ascites is commonly present.

Imaging

The classical imaging appearance mirrors the surgical findings: There are multiple tumours seen 'studding' the peritoneal cavity. Some patients may have more than 1000 of these tumours. No imaging modality has proven superiority.

Natural History

Even with treatment the prognosis of DSRCT is very poor. Five year survival is about 15%. Metastases to the liver occur and patients develop obstructive symptoms in the abdomen.

Tumour Features

Macroscopic Features

The tumour causes multiple peritoneal deposits which are visible at surgical resection. If cut, the surface is grey-white with areas of necrosis and haemorrhage.

Microscopic Features

Perhaps the best named of all tumours, DSRCT consists of variably sized nests of small, round cells that are grow within an abundant desmoplastic stroma (contains large amounts of connective tissue/collagen). The neoplastic cells have minimal cytoplasm and have no significant nuclear pleomorphism. Necrosis can be seen. The stroma is often highly vascular.

Genetics

The constant genetic finding is a translocation of chromosomes 11 and 22 - t(11;22). The translocation in all DSRCTs leads to the formation of a chimeric gene, fusing the EWSR1 (EWing Sarcoma breakpoint Region 1) gene on chromosome 22 with the WT1 (Wilms Tumour 1) gene on chromosome 11.

Staging / Classification

All DSRCTs are classified as stage 4 but there is no well defined staging system.


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