Rhabdomyosarcoma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Suveenkrishna Pothuru, M.B,B.S. [2]

Overview

Rhabdomyosarcoma arises from the skeletal muscle cells. Development of alveolar rhabdomyosarcoma is result of specific genetic mutations. The pathogenesis of rhabdomyosarcoma include t(2;13) and t(1;13) chromosomal translocations. The microscopic pathology of rhabdomyosarcoma depends on the histological subtype.

Pathophysiology

Histology

• The origin of rhabdomyosarcoma is muscle cells.
• The presentation sites of rhabdomyosarcoma are:
  • Head and neck (28%)
  • Extremities (24%)
  • Genitourinary tract (18%)
  • Trunk (11%)
  • Orbit (7%)
  • Retroperitoneum (6%)
  • Other sites such as bladder, vagina, nasopharynx, and middle ear (3%)

Genetics

Alveolar rhabdomyosarcoma

Specific genetic abnormalities have been identified, that are specific for alveolar rhabdomyosarcomas. They include t(2;13) and t(1;13) chromosomal translocations resulting in PAX3-FKHR and PAX7-FKHR gene fusions.

Microscopic Pathology

Characteristic features on microscopic analysis are variable depending on the rhabdomyosarcoma subtype:

Alveolar Rhabdomyosarcoma

• Characterized by Alveolus-like pattern.
• Fibrous septae lined by tumor cells.
  • Cells may "fall-off" the septa, i.e. be detached/scattered in the alveolus-like space.
  • Space between fibrous septae may be filled with tumor, called solid variant of alveolar rhabdomyosarcoma.
• Rhabdomyoblasts: Essentially diagnostic cells with eccentric nucleus and moderate amount of intensely eosinophilic cytoplasm.
• Nuclear pleomorphism
• Mitoses

Alveolar Rhabdomyosarcoma- intermediate magnification

Alveolar Rhabdomyosarcoma - high magnification

Embryonal Rhabdomyosarcoma

• Randomly arranged small cells
• Myxoid matrix
• Strap cells: Tadpole like morphology
• Rhabdomyoblasts: Essentially diagnostic cells with eccentric nucleus and moderate amount of intensely eosinophilic cytoplasm

Botryoid Rhabdomyosarcoma

• Malignant cells in an abundant myxoid stroma.
• Non-proliferating layer deep to the surface called "Cambium layer".
• Cambium layer is defined as cellular region deep to epithelial component.

Spindlecell Rhabdomyosarcoma

• Vesicular growth pattern
• Spindle cells