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Diagnosis in Oncology
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Desmoplastic Small Round-Cell Tumor of the Pancreas
A 35-year-old woman presented with progressive abdominal pain and weight loss over a period of 5 months. Clinical examination revealed a distended abdomen with liver enlargement. Contrast enhanced computed tomography scan revealed a mass in the tail of pancreas and the presence of at least two large liver metastases. A core biopsy of the liver showed a malignant small round-cell tumor, but no definitive diagnosis could be made due to small volume of biopsy material. An open biopsy of the pancreas was then undertaken and provided substantial fresh tissue to allow sampling for cytogenetic analysis. Light microscopic examination confirmed a malignant small round-cell tumor composed of irregular nests of small round cells set in a desmoplastic stroma (Fig 1A). Some of the cells showed round pink intracytoplasmic inclusions (Fig 1B). Immunohistochemically, the tumor cells were positive for low molecular weight cytokeratin, vimentin, epithelial membrane antigen, CD99, and desmin which exhibited characteristic dot positivity (Fig 1C). The tumor cells were negative for synaptophysin, chromogranin, CD56, CD3, CD20, S100 protein, Myo D1, smooth muscle actin, and Bcl2. Tumor cultures failed to produce metaphase cells for chromosome analysis. Interphase fluorescence in situ hybridization studies showed split signals for Vysis Ewing's sarcoma (EWS) gene break-apart probe in 72% of tumor nuclei, implicating 22q12 chromosome rearrangement (Fig 2A). Signal gains suggested a tetraploid chromosome complement. A Wilms' tumor (WT1) gene break-apart probe was developed by using P1 artificial chromosomes (PAC) clones RP4-760G15 and RP1-259N9 obtained from BACPAC Resources (Children's Hospital, Oakland Research Institute, Oakland, CA). Signals were split in the majority of nuclei, indicating a 11p13 chromosome rearrangement (Fig 2B). FISH findings were consistent with translocation t(11;22)(p13;q12). Real-time polymerase chain reaction using EWS and WT1 primers, generated a fusion transcript of the size expected for the fusion of these genes (Fig 2C). Sequencing of the polymerase chain reaction product confirmed the fusion of sequences from WT1 and EWS proving the diagnosis of desmoplastic small round-cell tumor (DSRCT; Fig 2D). As surgical resection was not viable at presentation, our patient underwent systemic therapy with vincristine 1.4 mg/m2 (maximum 2 mg) on day 1, doxorubicin 20 mg/m2, ifosfamide 3 g/m2 plus mesna and etoposide 150 mg/m2 on days 1 to 3, given every 21 days (VIDE regimen). However, despite treatment, her disease progressed after two cycles of chemotherapy. At this point, her performance status was starting to deteriorate. Her treatment regimen was subsequently changed to a regimen consisting of vinorelbine 25 mg/m2 on days 1, 8, 15 and cyclophosphamide 25 mg/m2 daily on a 28-day cycle.1 Disease stabilization was achieved after two cycles accompanied by significant improvement of her symptoms and general well-being.
DSRCT is a rare, aggressive mesenchymal tumor which occurs mainly in young adult males.2 This tumor is characterized by a unique karyotype aberration involving the fusion of EWS and WT-1 genes, as demonstrated by our patient.3 The resultant chimeric protein is thought to be a transcriptional activator that fails to suppress tumor cell growth.2,4 Clinically, this tumor often presents with pain associated with a large mass(es) within the abdominopelvic region. Its most common primary site is the peritoneum. Extraperitoneal involvement, such as in testes, ovaries, and pleura have been described in current literature pool.5 Involvement of the pancreas, as in the case of our patient, still remains an exceptional occurrence with only one known report previously.6 Prognosis of patients with this tumor is poor. Median survival ranges around 17 to 25 months, with very few patients experiencing prolonged survival.7 Management of this condition often involves a multimodality approach, but more than often with palliative intent. It has been shown that this tumor responds to alkylating agent-containing regimen in a dose-responsive manner. Aggressive, high-dose chemotherapy regimen including that of myeloablative chemotherapy with stem cell rescue may be useful in prolonging progression-free survival.8 Recently, the use of nonintensive chemotherapy, such as the vinorelbine/cyclophosphamide regimen, have been described to exert a therapeutic effect in DSRCT.1 However, its exact role in the treatment of this condition still remains undefined.
The authors indicated no potential conflicts of interest.
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