Case 138 - Discussion

Uploaded: 2007-10-28, Updated: 2007-11-02

 
  • Positive: Desmin
  • Negative: Cytokeratin, CD30, PLAP
 

Rhabdomyosarcoma

CLINICAL FEATURES
 
Embryonal Rhabdomyosarcoma
 
Alveolar Rhabdomyosarcoma
 
  • Second most common subtype, 31% of rhabdomyosarcomas;

  • Most frequently observed in adolescents, 10-25 years of age;

  • Most commonly in the deep tissue of the extremities, and accounts for approximately 50% of all extremity rhabdomyosarcomas;

  • On microscopy, the poorly differentiated round/oval tumor cells with scant indistinct cytoplasm are arranged in ill-defined aggregates. The individual aggregates are separated and outlined by a framework of dense fibrous/hyalinized septa that surround dilated vascular channels. The cells in the periphery of the cluster are well preserved and adhere to the fibrous septa, and the cells In the center of the clusters are arranged loosely, and therefore, they appear in an alveolar pattern. These cells stain intensely with eosinophilic stain. Multinucleated giant cells, multiple peripherally placed nuclei with pale or weakly eosinophilic cytoplasm. Cross-striated malignant rhabdomyoblasts are observed in 25% of cases, which is less frequent than what is observed with the embryonal form.

  • Alveolar rhabdomyosarcoma has distinct molecular characteristics, t(2;13)(q35;q14) (70%, PAX3 -FKHR ) and t(1;13)(p36;q14) (30%, PAX7-FKHR).

Pleomorphic Rhabdomyosarcoma

 
  • The least common of all subtypes, most often occurs in patients >45 years of age, mean 56 years. Rarely observed in children.

  • Most commonly seen in the deep soft tissue of the extremities;

  • Histologically, loosely arranged, haphazardly oriented, large, round or pleomorphic cells with hyperchromatic nuclei, deeply eosinophilic cytoplasm and multipolar mitotic figures. Rare cross-striations.

  • Positive for myogenic antigens (desmin, MSA, myoglobin, MyoD1), which are useful in differentiating this tumor from pleomorphic leiomyosarcoma and MFH.

IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS
 
  • Rhabdomyosarcomas contain glycogen and are positive for PAS stain;
  • Positive antibodies: desmin, sarcomeric alpha-actin, myoglobin, MyoD1.
ELECTRON MICROSCOPIC FINDINGS
 
  • Thin myofilament (actin), thick myofilament (myosin) and Z-bands.

TREATMENT AND PROGNOSIS
 
REFERENCES
 
  • Enzinger and Weiss's Soft Tissue Tumors, 4th Edition. By Drs. Sharon Weiss and John Goldblum.