Soft tissue

Uncertain differentiation

Desmoplastic small round cell



Topic Completed: 8 October 2021

Minor changes: 18 October 2021

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PubMed Search: Desmoplastic small round cell tumor[TI] review[ptyp]


Borislav A. Alexiev, M.D.
Page views in 2021 to date: 4,373
Cite this page: Alexiev BA. Desmoplastic small round cell. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissueDSRCT.html. Accessed October 20th, 2021.
Definition / general
  • Desmoplastic small round cell tumor (DSRCT) is a malignant mesenchymal neoplasm composed of small round tumor cells associated with prominent stromal desmoplasia, polyphenotypic differentiation and EWSR1-WT1 gene fusion
Essential features
  • Nests of small round cells in a desmoplastic stroma
  • Expression of cytokeratin, desmin and WT1 (antibody to carboxy terminus [C terminus])
  • EWSR1-WT1 fusion transcripts
Terminology
  • Intra-abdominal desmoplastic round cell tumor
ICD coding
  • ICD-0: 8806/3 - desmoplastic small round cell tumor
  • ICD-11: 2B5F.2 & XH5SN6 - sarcoma, not elsewhere classified of other specified sites & desmoplastic small round cell tumor
Epidemiology
Sites
Pathophysiology
  • Recurrent t(11;22)(p13;q12) translocation leading to formation of the EWSR1-WT1 fusion gene, which generates a chimeric protein with transcriptional regulatory activity (Int J Surg Pathol 2016;24:672)
Etiology
  • Unknown
Clinical features
  • Clinical symptoms are usually related to the primary site of presentation, such as pain, palpable mass, abdominal distention, obstruction and ascites (J Gastrointest Cancer 2019;50:560)
  • At initial presentation, 90% of patients have multifocal disease, nodular disease, diffuse peritoneal and omental disease or a combination of these conditions
  • Substantial number of patients have diaphragmatic involvement
Diagnosis
  • Tissue sampling is the gold standard for a definitive diagnosis
  • Fluorescence in situ hybridization (FISH) to detect EWSR1 rearrangement and reverse transcription polymerase chain reaction (RT-PCR) to assess for EWSR1-WT1 fusion transcripts are routine diagnostic ancillary tools (Virchows Arch 2017;471:631)
  • Both methods (FISH and RT-PCR) complement each other by confirming cases that the other method may not (Virchows Arch 2017;471:631)
Radiology description
Radiology images

Contributed by Borislav A. Alexiev, M.D.
CT Abdomen / pelvis

CT of abdomen / pelvis

Prognostic factors
Case reports
Treatment
  • Current management of DSRCT includes a combination of chemotherapy, radiation and aggressive cytoreductive surgery, plus intraperitoneal hyperthermic chemotherapy (Cancers (Basel) 2021;13:498)
Gross description
  • Typical gross appearance consists of multiple tumor nodules
  • Cut surface is firm and grayish white, with foci of necrosis and hemorrhage
Gross images

Contributed by Borislav A. Alexiev, M.D.
Multiple tumor nodules

Multiple tumor nodules

Frozen section description
  • Sharply outlined nests of small round, epithelioid or spindled cells surrounded by prominent desmoplastic stroma
Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Borislav A. Alexiev, M.D.
Well defined nests

Well defined nests

Desmoplastic stroma

Desmoplastic stroma

Uniform cells

Uniform cells

Mild anisonucleosis

Mild anisonucleosis

Large cell pattern

Large cell pattern


Desmin

Desmin

Keratin AE1 / AE3

Keratin AE1 / AE3

WT1 (C terminus)

WT1 (C terminus)

WT1 (N terminus)

WT1 (N terminus)

Cytology description
  • Hypercellular smears of small round cells (Cancer Cytopathol 2014;122:386)
  • Round or kidney shaped nuclei with inconspicuous nucleoli
  • Nuclear molding usually present
  • Scant cytoplasm
  • Paranuclear cytoplasmic densities
  • Numerous mitotic figures, crushed nuclei and apoptosis
  • Connective tissue fragments (Acta Cytol 2012;56:576)
Cytology images

Contributed by Borislav A. Alexiev, M.D.
Touch smear cytology

Touch smear cytology

Immunofluorescence description
  • EWSR1-WT1 break apart FISH demonstrates separation of signals indicative of translocation involving the EWS locus (Oncol Lett 2012;4:423)
  • Paired locus specific EWS and WT1 probes show EWSR1-WT1 fusion signals in nuclei of DSRCT (Oncol Lett 2012;4:423)
Immunofluorescence images

Contributed by Jose G. Mantilla, M.D.
EWSR1 gene break apart

EWSR1 gene break apart



Images hosted on other servers:

Fluorescence in situ hybridization

Positive stains
Electron microscopy description
Molecular / cytogenetics description
Sample pathology report
  • Peritoneum, biopsy:
    • Desmoplastic small round cell tumor (see comment)
    • Comment: The tumor is characterized by sharply outlined nests of small round cells surrounded by a prominent desmoplastic stroma. The tumor cells are uniform, with small hyperchromatic nuclei, inconspicuous nucleoli, scant cytoplasm and indistinct cytoplasmic borders. Mitoses are frequent and focal tumor cell necrosis is present. Immunohistochemically, the tumor cells are immunoreactive for keratin AE1 / AE3 and desmin and show strong nuclear expression for WT1 (C terminus), while all of the following are negative: myogenin, MYOD1, S100 and WT1 (N terminus). The findings support the above diagnosis. Despite multimodal treatment, DSRCT is associated with dismal outcomes.
Differential diagnosis
  • Blastemal predominant Wilms tumor:
    • Overlapping histologic features with DSRCT, including poorly differentiated morphology, desmoplastic stroma and immunoreactivity for desmin and cytokeratin (Am J Surg Pathol 2014;38:1220)
    • Focal triphasic elements and glomeruloid bodies
    • WT1 immunoreactivity with antibodies to both the amino terminus and carboxy terminus
    • Negative for EWSR1-WT1 rearrangements
  • Ewing sarcoma:
    • Classic Ewing sarcoma:
      • Composed of uniform small round cells with round nuclei containing finely stippled chromatin and inconspicuous nucleoli, and scant clear or eosinophilic cytoplasm
    • Atypical Ewing sarcoma:
      • Tumor cells are larger, with prominent nucleoli and irregular nuclear contours
  • Rhabdomyosarcoma, embryonal and alveolar variants:
    • Embryonal rhabdomyosarcoma
      • Composed of primitive mesenchymal cells that show variable degrees of skeletal muscle differentiation
    • Alveolar rhabdomyosarcoma
      • Classic subtype: nests of neoplastic cells arranged in alveolar spaces
      • Solid subtype: sheets of neoplastic cells; nests separated by thin fibrovascular septae but alveoli are not seen
    • Mogenin and MyoD1 positive
    • WT1 (C terminus) negative
    • PAX3-FOXO1 and PAX7-FOXO1 fusion transcripts (alveolar rhabdomyosarcoma) (Mod Pathol 2021;34:748)
    • Negative for EWSR1-WT1 rearrangements
  • Lymphoma:
    • Diffuse or nodular growth pattern, large atypical cells with abundant cytoplasm, nuclei with clumped chromatin and prominent nucleoli
    • Positive for CD45, B cell and T cell markers (Appl Immunohistochem Mol Morphol 2013;21:116)
    • WT1 (C terminus) negative
    • Negative for EWSR1-WT1 rearrangements
  • Small cell carcinoma:
Board review style question #1

A 31 year old man presented with abdominal distention and multiple tumor nodules studding the peritoneal surface. Hematoxylin eosin stains demonstrate well defined nests of small round cells separated by desmoplastic stroma. The tumor cells are uniform, with small hyperchromatic nuclei, inconspicuous nucleoli and scant cytoplasm. Mitoses are frequent and focal tumor cell necrosis is present. Perineural invasion is identified. Immunohistochemically, the tumor cells are immunoreactive for keratin AE1 / AE3, desmin, NSE and WT1 (C terminus), while all of the following are negative: myogenin, MYOD1, S100 and WT1 (N terminus). Which of the following is most likely the correct diagnosis?

  1. Desmoplastic small round cell tumor
  2. Ewing sarcoma
  3. Lymphoma
  4. Small cell carcinoma
  5. Wilms tumor
Board review style answer #1
A. Desmoplastic small round cell tumor

Comment Here

Reference: Desmoplastic small round cell
Board review style question #2
Which of the following is true about desmoplastic small round cell tumor?

  1. Desmoplastic stroma is always present
  2. Prognosis of DSRCT has improved considerably with current multimodal therapy
  3. Striking female predominance
  4. Tumor is positive for WT1 (N terminus)
  5. Widespread abdominal / peritoneal involvement is common
Board review style answer #2
E. Widespread abdominal / peritoneal involvement is common

Comment Here

Reference: Desmoplastic small round cell
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