Rhabdomyosarcoma
- Lesion
The commonest soft tissue sarcoma of children: a tumour of cells trying to become skeletal muscle, often in the head, neck or genital tract.
What it is
Rhabdomyosarcoma is a malignant tumour with skeletal muscle differentiation and the commonest soft tissue sarcoma of childhood and adolescence. It arises in the head and neck, the genitourinary tract and the limbs, often where skeletal muscle is scarce. The embryonal type affects young children; its botryoid variant grows as grape-like polyps under mucosa of the vagina, bladder or biliary tract. The alveolar type affects adolescents, is more aggressive and carries PAX3-FOXO1 or PAX7-FOXO1 fusions. Pleomorphic rhabdomyosarcoma is a tumour of older adults.
Structure
- Embryonal: sheets of small round and spindle cells in a myxoid stroma with scattered rhabdomyoblasts.
- Botryoid: polypoid tumour with a dense subepithelial cambium layer.
- Alveolar: fibrous septa forming spaces in which cells are discohesive and float, like alveoli; solid variants exist.
- Pleomorphic: large bizarre eosinophilic cells in older adults.
Step by step
- Muscle progenitors normally switch off PAX3/PAX7 as they differentiate.
- In alveolar rhabdomyosarcoma, the PAX-FOXO1 fusion keeps a powerful myogenic program on without maturation.
- In embryonal tumours, RAS pathway mutations and 11p15 loss drive proliferation.
- Cells express early muscle transcription factors (myogenin, MyoD1) but fail to form mature fibres.
- Tumours grow locally and spread to lymph nodes, lungs and bone marrow.
Markers
- Desmin
- Myogenin (MYF4) nuclear
- MyoD1 nuclear
- FOXO1 rearrangement (alveolar)
Clinical notes
- Child with proptosis, nasal obstruction or a grape-like mass protruding from the vagina: think of rhabdomyosarcoma.
- Treated with chemotherapy plus surgery and/or radiation; embryonal tumours in favourable sites do well.
- Associated syndromes: Li-Fraumeni, NF1, Beckwith-Wiedemann, Costello.
Test yourself
Think of the answer, then tap the question to see it.
Which nuclear markers confirm skeletal muscle differentiation?
Myogenin and MyoD1 (with cytoplasmic desmin).
Which fusion defines alveolar rhabdomyosarcoma?
PAX3-FOXO1, t(2;13), or PAX7-FOXO1, t(1;13).
What is the cambium layer?
A dense band of tumour cells just beneath the epithelium in botryoid rhabdomyosarcoma.
Which type has the worse prognosis, embryonal or alveolar?
Alveolar.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Childhood Rhabdomyosarcoma Treatment (PDQ®) - NCI (National Cancer Institute, 2025).
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Representative model, for educational purposes only.