Synonyms

• ARMS
• alveolar-type rhabdomyosarcoma

Category

Soft tissue

Behaviour

Malignant

Grade

High

Gender

Both equally

Tissue of Origin

Skeletal muscle

Epidemiology

• High-grade embryonal rhabdomyosarcoma subtype
• Peak incidence in older children than embryonal rhabdomyosarcoma
• Peak incidence 10-25 years
• More aggressive than embryonal type

Clinical Features

• Rapidly growing deep soft tissue mass
• Metastases often present at diagnosis (25-30%) via lymphatic or haematogenic spread

Location

• Extremities most common
• Trunk and paraspinal region
• Head and neck

Imaging

• MRI primary site with gadolinium - local staging
• CT chest/abdomen/pelvis - metastatic staging

Pathology

• Nested architecture with PAX-FOXO1 fusion
• Small round cells with myogenic features
• Higher grade than embryonal type

Genetics

PAX3-FOXO1 (t(2;13)) or PAX7-FOXO1 (t(1;13)) translocations

Treatment

• Intensive multiagent chemotherapy (VAC/IE)
• Local control: surgery and/or radiotherapy
• Stem cell rescue for High-risk disease

Prognosis

• 50% 5-year survival for alveolar subtype
• Worse than embryonal subtype
• Fusion-positive ARMS has worse prognosis
• Metastatic disease at diagnosis significantly impacts prognosis

Key Points

• PAX-FOXO1 positive alveolar RMS is high-risk
• Older age of presentation than embryonal
• More aggressive and higher metastatic potential

Workup - Blood Tests

• FBC, U&E, LFTs - baseline and pre-chemo
• LDH - prognostic marker

Workup - Local Imaging

MRI with contrast of primary site

Workup - Biopsy

• Core needle biopsy - confirm diagnosis
• PAX-FOXO1 FISH - prognostic risk stratification

Workup - Staging

• CT chest/abdomen/pelvis - metastases
• PET-CT - staging

Workup - Other

• Paediatric oncology MDT mandatory
• Intensified chemotherapy and local therapy required

Follow-up Summary

• Post-operative review at 6 weeks
• Year 1: 2-monthly clinical examination, CXR, plain films of primary bony site; soft tissue tumours - baseline end-of-treatment MRI/CT primary site, thereafter at clinician's discretion; radiotherapy as definitive local treatment - baseline end-of-treatment MRI/CT, then at 6 and 12 months; end of Year 1 - gonadal function and renal function
• Years 2–3: 3-monthly clinical examination, CXR, plain films of bony primary site; MRI of soft tissue primary site at clinician's discretion; radiotherapy patients - MRI/CT at 18 and 24 months; MUGA/ECHO 2 years post-diagnosis; annual renal function
• Year 4: 6-monthly clinical examination, CXR, plain films of primary site; MRI of soft tissue primary at clinician's discretion; MUGA/ECHO 4 years post-diagnosis; annual renal function
• Year 5: 6-monthly clinical examination, CXR, plain films of primary site; annual renal function
• Years 6–10: Annual clinical examination, CXR, plain films of primary site; MUGA/ECHO 6 years post-diagnosis; annual renal function
• Discharge at 10 years after surgery