Rhabdomyosarcoma (RMS)
Description
Rhabdomyosarcoma (RMS) is an embryonal malignancy derived from primitive mesenchymal cells, the same embryologic origin as striated muscle. It belongs to the small round blue cell tumour family based on light microscopy.
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Represents ~50% of all pediatric soft tissue sarcomas
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Two-thirds occur in children <6 years
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Slightly more common in males
WHO 2013 Histological Classification
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Embryonal RMS (ERMS) – fusion-negative
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Alveolar RMS (ARMS) – associated with PAX-FOXO1 fusions
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Pleomorphic RMS (PRMS)
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Spindle cell/Sclerosing RMS (SRMS)
Genetic Notes
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60% of ARMS: PAX3-FOXO1, t(2;13)
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20% of ARMS: PAX7-FOXO1, t(1;13)
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Remaining ARMS: rare or fusion-negative
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ERMS: fusion-negative
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Extremity tumours have the worst prognosis
Anatomical Distribution and Patterns of Spread
Primary Sites, Frequencies, and Metastatic Patterns
| Primary Site | Frequency | Metastatic Pattern |
|---|---|---|
| Head and neck | 34% | — |
| Orbit | 8% | — |
| Non-parameningeal | 8% | — |
| Parameningeal | 18% | CNS |
| Genitourinary | 25% | — |
| Paratesticular/Vagina/Uterus | 12% | Lymphatic |
| Bladder/Prostate | 11% | — |
| Extremity | 15% | Lymphatic + Haematogenous |
| Other sites | 25% | — |
Abbreviations: CNS = Central nervous system; GU = Genitourinary; NPM = Non-parameningeal; PM = Parameningeal
Investigations
A. Imaging
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MRI of primary site + lymph nodes
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CT of primary site + lymph nodes
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CT chest
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PET scan or bone scan or skeletal survey for staging
B. Biopsy & Laboratory Tests
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Biopsy of primary tumour
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Immunohistochemistry: MyoD1, Desmin, Myogenin, MSA
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Bilateral bone marrow aspirate/biopsy
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Lumbar puncture for CSF cytology (PM/paraspinal tumours)
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RT-PCR & FISH using FOXO1 probe for PAX-FOXO1 fusions
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FBC, LFTs, Urea, Creatinine
Treatment
Risk-adapted therapy
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Chemotherapy with VAC regimen
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Alternating VDC with IE
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Total duration: 39 weeks (13 VDC/IE cycles)
VAC Regimen
| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Vincristine | 1.5 mg/m² | IV push | Day 1 |
| Actinomycin D | 0.05 mg/kg | IV push | Day 1 |
| Cyclophosphamide | 1200 mg/m² | IV infusion (≥30 mins) | Day 1 + MESNA 20% of dose IV ×3 doses q4h |
VDC Regimen
| Drug | Dose | Route | Frequency | Schedule |
|---|---|---|---|---|
| Vincristine | 1.5 mg/m² | IV | OD | Day 1, 8, 15 |
| Doxorubicin | 30 mg/m² | IV | OD | Day 1, 2 |
| Cyclophosphamide | 600 mg/m² | IV | OD | Day 1, 2 |
IE Regimen
| Drug | Dose | Route | Frequency | Schedule |
|---|---|---|---|---|
| Ifosfamide | 1800 mg/m² | IV | OD | Day 1–5 |
| MESNA | 20% of total Ifosfamide dose | IV | Every 4 hours ×3 | Day 1–5 |
| Etoposide | 100 mg/m² | IV | OD | Day 1–5 |
| Filgrastim | 5 mcg/kg/day | SC | OD | Day 7–14 |
Palliative Oral Metronomic Therapy (12 cycles)
| Drug | Dose | Schedule |
|---|---|---|
| Oral Etoposide | 50 mg/m² daily | 3 weeks on → 7–10 days off |
| Oral Cyclophosphamide | 2.5 mg/kg daily | 3 weeks on → 7–10 days off |