A desmoplastic small round blue cell tumor (DSRCT) is a very rare soft tissue sarcoma tumor, usually arises from intra-abdominal mesenchymal tissues and it has very aggressive clinical behavior. Since the first case of DSRCT reported in 1989 by Gerald and Rosai [1], approximately 500 cases have been described in the literatures [2],[3].

Desmoplastic small round blue cell tumors mainly present in children and young adults. The main symptoms are related to widespread intra-abdominal disease. Almost all patients have peritoneal metastases at presentation, and approximately half of the presenting patients have extra-peritoneal metastases (EPM) [3]. Diagnosis depends on correlation of clinical presentation with positivity of different immunohistochemical (IHC) markers (epithelial, mesenchymal, neural, and muscle), but the most characteristic marker is the presence of the EWS-WT1 protein [4],[5]. The prognosis of this type of sarcoma is dismal. Despite the use of different treatment modalities, including surgery, radiation, and chemotherapy, the 5-year survival is still around 15% [6].

We present a case of a very rare soft tissue sarcoma in a young Saudi male patient who was diagnosed from a biopsy obtained from a metastatic site (liver) rather than the primary site.

Patient information

A 32-year-old male patient without known medical disease presented to our hospital with rapidly progressive abdominal distension of two months duration associated with mild dull aching abdominal pain and weight loss of 1 kilogram.

Clinical findings

His clinical examination was remarkable for tense ascites, and an ill-defined abdominal mass was found in the umbilical area.

Diagnostic assessment

Initial workup showed mild thrombocytosis but blood counts, liver, and renal function were normal.

His initial workup was based on abdominal ultrasound and showed ascites and multiple liver masses, so the patient had an abdominal computed tomography (CT) scan with contrast, which revealed a large, predominantly cystic mass measuring 16.5 × 15 × 12.5 cm arising from the mesentery that had displaced the small bowel loops. In addition, the CT showed ascites, multiple peritoneal nodules, and cystic liver metastases (Figure 1).

Because of the tense ascites, 4 L was aspirated and was sent for cytological examination, which showed the presence of atypical cells. The patient underwent ultrasound (US)-guided biopsy from the liver mass. A sheet of round small cells was observed. Based on the liver biopsy, our pathologist recognized a desmoplastic stroma between the cells.

IHC method

Immunohistochemistry was performed at King Fahad General Hospital histopathology laboratory using the Ventana Discovery XT. Briefly, 4 μm paraffin sections were deparaffinized. Tris-EDTA buffer pH 7.8 at 95 °C for 44 min was used for antigen retrieval. Primary antibodies were incubated for 1 hour whereas horseradish peroxidase (HRP)-conjugated secondary antibodies were incubated for 16 minutes. DAB was applied for 8 minutes followed by 8 minutes of counterstain with hematoxylin. Slides were dehydrated and coverslipped.

The malignant cells showed strong positive desmin and were weakly positive for pan-cytokeratin (CK-pan), cluster of differentiation (CD)99, and CD56 but negative for CD45, low-molecular weight cytokeratin (LMWCk), S100, and neuron-specific enolase (NSE) (Figure 2). A diagnosis of an abdominal desmoplastic small round blue cell tumor (DSRCT) with liver metastases was made.

Therapeutic intervention, follow-up, and outcomes

Since this tumor is very rare, we referred the patient to a hospital specialized in treating such rare tumors in the kingdom. Pathology was reviewed in the accepted hospital, and it is concurred with our diagnosis.

Desmoplastic small round blue cell tumor is a very rare soft sarcoma and presents a highly aggressive clinical course that affects mainly young males of Caucasian ethnicity [7]. It was first described by Gerald and Rosai in 1989. They described a tumor with characteristic features containing small blue round cells that are surrounded by desmoplastic stroma. Those cells can express epithelial, neuronal, and mesenchymal markers. Up to now, approximately 500 cases of DSRCT have been reported in the literature. To the best of our knowledge, only five DSCRT cases have been reported in Saudi Arabia (two intra-abdominal, one ovarian, one stomach, and one pancreatic).

Desmoplastic small round blue cell tumors are typically seen in the abdominal or pelvic cavity in 90% of patients, but a wide spectrum of rare sites including testis, pleura, stomach, pancreases, kidney, sinus, and brain have been reported [7],[8].

Desmoplastic small round blue cell tumor is a disease of adolescent males with a male to female ratio of 4:1. The usual presentation of most of cases is in the second or third decade of life [9]. Since the most common site of a DSRCT is intra-abdominal, most patients present with gastrointestinal symptoms. Unfortunately, those symptoms occur when the tumor is at an advanced stage as seen in our case. At this point, approximately half of patients present with metastases, and the most common metastases are liver, lung, and lymph nodes [2],[8].

Imaging studies in DSRCT do not show specific findings, but these findings suggest this disease when a young patient presents with an abdominal or pelvic mass with extensive peritoneal disease and ascites without definitive organ involvement [7]. The dominant mass is lobulated, solid, and shows a retrovesical or rectouterine location with an average size of 12 mm in more than 50% of patients [10]. Our patient presented with a huge abdominal mass (16 cm) with peritoneal nodules, ascites, and liver metastases. The mass in our patient has a cystic component, and its location is not a typical radiological feature. In a small retrospective study, it was found that fluorodeoxyglucose-positron emission/computed tomography (FDG-PET/CT) showed superiority to conventional imaging for detecting disease burden, and in another study, it was found that PET/CT has advantages over conventional imaging for detecting isolated relapses [10].

Even after a biopsy of a DSRCT tumor, the diagnosis may still be challenging because, microscopically, the tumor appears as round blue cells with the possibility for many differential diagnoses, for example, Ewing’s sarcoma. However, the presence of extensive collagenous stroma points to the correct diagnosis. Furthermore, by using IHC, the tumor was shown to co-express many marker (epithelial, mesenchymal, neural, and muscle). In our case, the biopsy was taken from the metastatic site (liver). The most important confirmatory test, which is found in more than 90% of patients, was the presence of the translocation t(11;22) (p13;q12) and detection of EWS-WT1 gene by reverse transcriptase polymerase chain reaction [4],[5].

Unfortunately, no standard treatment for DSRCT is available to date because of the very rare nature of the tumor, which makes it extremely difficult to conduct clinical trials. Furthermore, no validated staging system exists for comparing different treatment approaches of this tumor. The recommendation of multimodal treatment consisting of surgery, radiation, and chemotherapy in suitable patients is based on retrospective studies. Lal et al. reported that the 3-year survival for patients who were treated with induction chemotherapy (P6), debulking surgery, and radiotherapy is 55% compared with only 27% in those who are not treated with this method. Despite this difference and even after using the aggressive approach for treating these tumors, the prognosis is dismal and the 5-year survival is only 15%. In recent retrospective study, the 5-year survival reported is only 25% by using multidisciplinary treatment [9].

We present a case of a DSCRT, a rare soft tissue sarcoma, which is a highly aggressive tumor. Its diagnosis may be challenging and needs the correlation of clinical, radiological, morphological, immunohistochemical, and even genetic data to reach a diagnosis, especially in atypical presentations.