Desmoplastic small round cell tumor
Synonyms and keywords: Desmoplastic small round cell tumour; Desmoplastic small round blue cell tumor; Desmoplastic small round blue cell tumour; Intraabdominal desmoplastic small round blue cell tumor; Desmoplastic small cell tumor; Desmoplastic cancer; Desmoplastic sarcoma; DSRCT; Mesothelioblastoma; Polyphenotypic small round cell tumor

# Overview
Desmoplastic small round cell tumor is an extremely rare, highly aggressive, and malignant neoplasm initially reported by Gerald and Rosai in 1989. The pathogenesis or histogenesis of desmoplastic small round cell tumor is uncertain; it mainly occurs in adolescents and mostly involves the abdominal and/or pelvic peritoneum. Moreover, it was also reported in epididymis, pleura, soft tissues, bone, ovary, and kidney. The diagnosis can be confirmed by histological and immunohistochemistry studies. CT scan is the most widely used diagnostic modality; abdominopelvic site was the commonest presentation and the disease can occur at other nonserosal surfaces also. Despite multimodality treatments, optimal treatment strategies remain controversial and the prognosis is poor. Current multimodality treatment rarely achieves cure and prolongs life. Here, we described 12 cases of abdominal DSRCT and retrospectively analyzed its clinical, radiological, and biopathological features, highlighting the modalities of treatment

# Historical Perspective
Desmoplastic small round cell tumor was first described by pathologists, William L. Gerald and Juan Rosai, in 1989. but as a distinct entity in 1991.

# Pathophysiology

## Pathogenesis
Desmoplastic small round cell tumor is a highly aggressive, rare tumor of mesenchymal origin whose oncogenic effect is presumed to originate from the unique chromosomal translocation t(11;22)(p13:q12), leading to the fusion of the N-terminal domain of Ewings sarcoma gene EWS, to the C-terminal domain of Wilms tumor suppressor gene, WT1, which is found in most but not all desmoplastic small round cell tumors.

## Genetics
Desmoplastic small round cell tumor is associated with a unique chromosomal translocation t(11;22)(p13:q12), resulting in an EWS/WT1 transcript that is diagnostic of this tumor. This transcript codes for a protein that acts as a transcriptional activator that fails to suppress tumor growth. The EWS/WT1 translocation product targets ENT4. ENT4 is also known as PMAT.

## Associated Conditions
There may be a chimeric relationship between desmoplastic small round cell tumor, and Wilms' tumor and Ewing's sarcoma. Together with neuroblastoma and non-Hodgkin's lymphoma, they form the small cell tumors.

## Microscopic Pathology
On microscopic histopathological analysis, desmoplastic small round cell tumor is characterized by:
- Broad bands of paucicellular fibrous stroma
- Small round cells in nests with an undulating sharp border
- The small round cells lack distinct nucleoli and have scant cytoplasm; they are small round cell tumor cells.
- Abundant mitoses
- +/-Necrosis
- Hyperplastic blood vessels

## Immunohistochemistry
Desmoplastic small round cell tumor is demonstrated by positivity to tumor markers, such as:
- AE1/AE3
- Desmin
- Vimentin
- EMA
- Neuron-specific enolase (NSE)
- WT1 (C-terminal)
- CD57

# Causes
Common causes of desmoplastic small round cell tumor include genetic mutations. A chromosomal translocation, t(11;22)(p13:q12) resulting in an EWS/WT1 transcript, may result in formation of desmoplastic small round cell tumor. This transcript codes for a protein that acts as a transcriptional activator that fails to suppress tumor growth. The EWS/WT1 translocation product targets ENT4. ENT4 is also known as PMAT.

# Differentiating Desmoplastic Small Round Cell Tumor from other Diseases
- Desmoplastic small round cell tumor in the abdomen may cause gastrointestinal symptoms and mimic other abdominal tumors. So, they must be differentiated from other tumors in the abdomen, such as:
- Rhabdomyosarcoma
- Neuroblastoma
- Mesenteric carcinoid
- In older patients, desmoplastic small round cell tumor must be differentiated from:
- Non-Hodgkins lymphoma
- Peritoneal mesothelioma
- Peritoneal carcinomatosis
- In males, desmoplastic small round cell tumor may be mistaken for testicular germ cell tumor while in females, desmoplastic small round cell tumor may be mistaken for ovarian cancer.
- Desmoplastic small round cell tumor must be differentiated from other small-round blue cell cancers, such as:
- Ewing sarcoma
- Neuroblastoma
- Embryonal rhabdomyosarcoma
- Pineoblastoma
- Wilms tumor
- Retinoblastoma
- Hepatoblastoma
- CNS primitive neuroectodermal tumor (CNS-PNET)
- Peripheral primitive neuroectodermal tumor (pPNET)
- Askin tumor
- Neuroepithelioma
- Acute leukemia
- Small cell mesothelioma

# Epidemiology and Demographics

## Incidence
- Age-adjusted incidence rate of desmoplastic small round cell tumor for African Americans and Caucasians is 0.05  and 0.02 per 100,000 individuals, respectively.
- The overall age-adjusted incidence rate of desmoplastic small round cell tumor is 0.03 per 100,000 individuals, with a peak incidence of 0.074 per 100,000 individuals in the 2024 years of age group.

## Age
- Desmoplastic small round cell tumor is a rare disease that tends to affect children and young adults.
- Peak age of incidence for desmoplastic small round cell tumor is between 20 and 24 years.

## Gender
Males are more commonly affected with desmoplastic small round cell tumor than females. The male to female ratio is approximately 4 to 1.

## Race
Desmoplatic small round cell tumor usually affects individuals of the African American and Caucasian race. Latin American and Asian individuals are less likely to develop desmoplatic small round cell tumor.

# Risk Factors
There are no established risk factors for desmoplastic small round cell tumor

# Natural History, Complications, and Prognosis

## Natural History
Because the disease can be misdiagnosed or remain undetected, tumors frequently grow large within the abdomen and metastasize or seed to other parts of the body.

## Complications
Complications of desmoplastic small round cell tumor include:
- Peritoneal seeding
- Lymph nodal involvement
- Metastasis (liver, bone, lung)

## Prognosis
- The prognosis for desmoplastic small round cell tumor remains poor and depends upon the stage of the cancer.
- The 5-year overall survival rate of patients with desmoplastic small round cell tumor is approximately 15%.

# Diagnosis
The diagnosis constitutes 

## Symptoms
- There are few early warning signs that a patient has a desmoplastic small round cell tumor.
- Patients are often young and healthy as the tumors grow and spread uninhibited within the abdominal cavity. These are rare tumors and the symptoms are often misdiagnosed by physicians. The abdominal lump may grow to enormous size before being noticed by the patient.

### Common Symptoms
Common symptoms of desmoplastic small round cell tumor include:
- Abdominal distention
- Lump in abdomen
- Abdominal pain
- Vomiting
- Back pain
- Gastrointestinal obstruction
- Lack of appetite
- Fatigue
- Weakness
- Cachexia

### Less Common Symptoms
Less common symptoms of desmoplastic small round cell tumor include:
- Unknown lumps
- Thyroid conditions
- Hormonal problems
- Blood clotting problems
- Kidney or urological problems
- Lump in the testicle, breast, uterus, vagina, or ovary

## Physical Examination
Common physical examination findings of desmoplastic small round cell tumor include:
- Palpable adominal mass
- Ascites
- Increased abdominal girth

## CT
- Abdominal CT scan is the most widely used diagnostic modality for desmoplastic small round cell tumor.
- Findings on CT scan suggestive of desmoplastic small round cell tumor include a solitary to multiple soft tissue masses with no definite organ of origin, usually in the retrovesical or rectouterine space, which enhance heterogenously on contrast studies. Necrosis, hemorrhage, and fibrous components are common.
- Peritoneal seeding, lymph nodal involvement, liver and bone metastases may also be demonstrated.

## MRI
- MRI may helpful in delineating the extent of desmoplastic small round cell tumor, if surgery is considered.
- On MRI, desmoplastic small round cell tumor is characterized by hypo- to isointensity on T1-weighted images. On contrast administration, it has a heterogenous enhancement, due to the fibrous stroma and degenerative features including necrosis, hemorrhage, and calcification.

# Treatment
Treatment includes
- Desmoplastic small round cell tumor is frequently misdiagnosed. Adult patients should always be referred to a sarcoma specialist. This is an aggressive, rare, fast spreading tumor and both pediatric and adult patients should be treated at a sarcoma center.
- Surgical excision with combination chemotherapy as an adjunct is mandatory for nonmetastatic cases because these modalities used in isolation may have less impact.
- There is no standard protocol for desmoplastic small round cell tumor; however, recent journals and studies have reported that some patients respond to high-dose (P6 Protocol) chemotherapy, maintenance chemotherapy, debulking procedure, cytoreductive surgery, and radiation therapy.
- Other treatment options for desmoplastic small round cell tumor include hematopoietic stem cell transplantation, intensity-modulated radiation therapy, radiofrequency ablation, stereotactic body radiation therapy, intraperitoneal hyperthermic chemoperfusion, and clinical trials.