Testis & epididymis
Spermatic cord tumors
Rhabdomyosarcoma -Spindle cell

Topic Completed: 1 July 2014

Minor changes: 3 July 2020

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PubMed Search: Rhabdomyosarcoma spindle cell testis

Related topics: Rhabdomyosarcoma

Swapnil U. Rane, M.D.
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Cite this page: Rane S. Rhabdomyosarcoma -Spindle cell. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/testisrmsscv.html. Accessed August 8th, 2020.
Definition / general
  • More differentiated with higher proportion of cases expressing markers of mature muscles (myoglobin, troponin T and muscle specific actin) compared to nonspindle cell variants (Am J Surg Pathol 1993;17:221)
    • The more mature nature of spindle cell RMS is also evident on ultrastruture, with a more uniform presence of thick and thin filaments within the spindle cells
    • Presence of large amounts of collagen also correlates with other markers of differentiation
Clinical features
  • Usually nontender scrotal mass, stage I / II at presentation
  • Less likely to metastasize (16%) than nonspindle cell variant (~31%) (Am J Surg Pathol 1993;17:221)
  • Better survival (88%) than patients with spindle cell RMS in other locations (58%) in the IRS I & II studies
  • No specific laboratory features
Radiology description
Prognostic factors
  • Similar to RMS in general
  • IRS I & II studies found a significantly better 5 year survival (95.5%) for the spindle cell variant as compared to the nonspindle cell variants (80%) of embryonal RMS (Am J Surg Pathol 1993;17:221)
Case reports
  • Surgical excision followed by chemotherapy ± radiotherapy
Gross description
Microscopic (histologic) description
  • Predominant cell type is elongated, spindle cell arranged in fascicles or whorls; herringbone growth pattern may be seen
  • Cells have eosinophilic fibrillar cytoplasm, centrally located nuclei with blunted or fusiform ends, small to inconspicuous or prominent nucleoli
  • Mitotic figures are easily appreciated, including atypical forms
  • A smaller proportion of admixed immature rhabdomyoblasts are usually seen, with bright cytoplasmic eosinophilia, eccentric nuclei and occasionally cytoplasmic cross striations (useful for diagnosis and to differentiate from leiomyosarcoma)
  • Variable collagen fibers intermingled between the spindle cells
  • Some authors, including the IRS I & II studies, identified collagen rich and collagen poor spindle cells
    • Collagen poor: cells are arranged in bundles or fascicles with abundant cellularity and little or no stroma, resembling leiomyosarcoma
    • Collagen rich: lower cellularity due to abundant fine collagen fibers with a "storiform" pattern giving it a more sclerotic appearance
    • This subclassification does not appear to affect clinical outcome
  • A mixture of histological types with nonspindle cell embryonal RMS, pleomorphic RMS or even alveolar RMS may be seen; the nomenclature of such cases is dependent on the proportion of each subtype in a given case
Microscopic (histologic) images

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Case of Week #145




AE1 / AE3

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With anaplasia

Virtual slides

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Spindle cell RMS from head and neck

Cytology description
  • Numerous spindle cells and large fragments of cytoplasmic processes with cross striations (Acta Cytol 2005;49:331)
Positive stains
Negative stains
Molecular / cytogenetics description
  • PAX3-FKHR / PAX7-FKHR fusion (RMS1 / RMS2) associated with alveolar RMS are classically absent
  • Cytogenetically, spindle cell RMS is close to embryonal RMS, based on presence of sporadic small gains of chromosome 2, 8, 11, 13 & 20
Differential diagnosis
  • Fibrosarcoma: herringbone pattern, may have similar morphology but no rhabdomyoblasts, negative for skeletal muscle markers
  • Infantile fibromatosis: deep location, fascicles of spindle cells, no cross striations and no undifferentiated cells
  • Leiomyosarcoma: usually high grade, cigar shaped nuclei, no rhabdomyoblasts, often positive for caldesmon and negative for myoglobin
  • Neuromuscular hamartoma of soft tissue: usually age < 2 years, affects brachial plexus or sciatic nerve, multinodular growth with connective tissue separating nodules, no rhabdomyoblasts, muscular component is positive for desmin and muscle specific actin and neural component is positive for S100
  • Rhabdomyoma: benign tumor of skeletal muscle differentiation, no rhabdomyoblasts, no pleomorphism, no necrosis
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