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Synovial Sarcoma Histology

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  • Histologic types:
    o Biphasic
    o Monophasic fibrous
    o Monophasic epithelial
    o Poorly differentiated
  • Epithelial cells resemble carcinoma
  • Spindle cells are not stromal cells, but tumor cells as well
  • Rarely have > 2 mitoses/HPF except poorly differentiated lesions
  • Calcifications or osseous metaplasia may be sparse or very prominant
  • Mast cells typically seen
  • Vascularity may be prominant and hemangiopericytoma-like
  • ±?lack of cellular cohesion forming pseudoalveolar pattern
  • ±?nuclear palisading
  • ±?pseudorosettes
  • ±?myxoid changes
  • Rarely with round cells as in Ewing sarcoma
  • Special stains:
    o Epithelial cell secretions:
    + + PAS
    + + for colloidal Fe++
    + + alcian blue
    + + mucicarmine
    o Spindle cell mucin:
    + + for colloidal Fe++ and alcian blue
  • Cytogenetics:
    o Translocation: t(X;18)(p11.2;q11.2) can be diagnostic in poorly differentiated lesions (t(X;18) not specific for synovial sarcoma)
    o Fusion of SYT gene on 18q11.2 with either SSX1 or SSX2 gene on Xp11.2
    + SSX2 identified as the cancer testis antigen HOM-Mel-40
  1. Some melanoma pts have IgG antibody immune responses specific for SSX2
  • SSX2 expression in tumor samples
    o 50% of melanoma samples
    o 30% of hepatocellular carcinoma samples
    o 25% of colon and prostate samples
    o 20% of breast cancers
    o Indicates SSX2 is upregulated independently from fusion events with SS18
    + SSX homologues
  1. SSX1
  2. SSX2
  3. SSX3
  4. SSX4
  5. SSX5
  6. SSX6
  7. SSX7
  8. SSX8
  9. SSX9
  10. ?SSX10
  • Only one not on the X chromosome
  • Located on chromosome 6
    o bcl-2 overexpression
    o 69% with SMARCB1/INI1 mRNA expression reduced
    + A suggested post-transcriptional SMARCB1/INI1 regulatory mechanism proposed
    o Chromogenic in situ hybridization (CISH)
    + Dual-color break-apart chromogenic in situ hybridization using dual-color break-apart probes to detect chimeric gene transcripts
  1. SS18-SSX1
  2. SS18-SSX2
  • Immunochemistries:
    o + cytokeratin typically seen in the spindle cell component
    o + epithelial membrane antigen
  • EM:
    o Epithelial cells:
    o Dense chromatin within nuclei, prominent Golgi, with junctional complexes interconnecting cells
  • Spindle cells:
  • Early epithelial differentiation

Mayo Clinic, Phoenix, Arizona



Date Added: 03-Jan-2011


Christopher Beauchamp
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