Rhabdomyosarcoma in Children

What is Rhabdomyosarcoma?

It is a rare and aggressive soft tissue sarcoma. Other genetic syndromes associated with rhabdomyosarcoma are given below:

• NF-1
• Li-Fraumeni Syndrome
• Beckwith - Weidemann syndrome
• Gorlin syndrome / Basal cell nevus syndrome
• Noonan syndrome
• APC gene mutations
• Werner syndrome
• Nijmengen breakage syndrome
• Hereditary Retinoblastoma

Histological Subtypes of Rhabdomyosarcoma

Embryonal Subtype

60% of childhood Rhabdomyosarcoma. Intermediate to good prognosis Head and neck, GU system

Alveolar Subtype

25%–40% of all Rhabdomyosarcoma. Poor prognosis, trunk, extremities.

Pleomorphic is an adult form—1-2% of the Rhabdomyosarcoma.

Also read: Neonatal Hypocalcemia

Embryonal Rhabdomyosarcoma

Cells are arranged loosely in edematous stroma. Variant called Sarcoma Botryoides (grape-like masses) Loss of heterozygosity of the 11p gene.

Alveolar Rhabdomyosarcoma

Alveoli likes patterns of arrangement. The fusion proteins (PAX3 FOXO-1 and PAX7 FOXO-1). They have a high incidence of translocation (1,13) (2,13).

Embryonal vs Alveolar RMS

• Both are positive for Actin and Desmin.
• Myogenin expression is used to distinguish between alveolar and embryonal RMS.
• Patchy - Embryonal RMS
• Diffuse, Strong, Alveolar RMS
• Both are Positive for Actin and Desmin

Also read: Rare Cancers in Children

Clinical Features: Rhabdomyosarcoma

The clinical features are heterogeneous. Site of origin (most common): Head & Neck > GU > Extremities > Other parts.

1. Asymptomatic mass / swelling: Limbs—apparent after trauma

2. Obstructive symptoms: Airway → Obstruction, Middle ear → OM, Ear pain, CNS → CN palsies

3. Orbital RMS → Proptosis, Strabismans

4. Botryoid → “Bunch of grapes” Vagina/bladder/middle ear

5. Constitutional symptoms

6. Site of metastasis → Pulmonary: Sarcoma Botryoides (grape-like masses)

Diagnosis

Two steps for diagnosing RMS: clinical suspicion and imaging, including CT scan, MRI, ultrasound, and PET. Biopsy- Gross appearance: alveolar or embryonic. Microscopy: small round blue cells with tadpole-like cells (myoblasts). Positive for muscle-specific markers like Desmin and actin.

COG Staging in Rhabdomyosarcoma

Favourable sites: Female genital, male paratesticular, head and neck

T1: confined to site of origin; T2: Any spread or fixation of mass

Site a: <5 cm, size b: ≥5 cm

Also read: Langerhans Cell Histiocytosis in Children

COG Risk Stratification for Rhabdomyosarcoma

Three groups are defined based on stage, histology, and group. The group is classified into low-risk, intermediate, and high-risk groups. Low risk: chemotherapy using vincristine, Actinomycin D, and ± cyclophosphamide.

Surgery: Surgery followed by radiotherapy can be given for residual disease. Intermediate risk: chemotherapy combined with three to four drugs (Vincristine, Actinomycin D, and Cyclophosphamide + Irinotecan) + radiotherapy. High risk has poor outcomes despite all the modalities.

Prognosis

Depends upon the stage or histology. Head and neck involvement, especially orbits, have good outcomes. Genital and urinary tract have good outcomes. Extremity tumors and alveolar histology have poor outcomes. If there is a residual disease after surgery followed by chemotherapy, poor outcome.

Important Points to Remember

• 60% of childhood Rhabdomyosarcoma. Intermediate to good prognosis Head and neck, GU system.
• Tadpole-like cells are seen under the microscope. Tadpole-like cells are a type of myoblast. They have an elongated appearance with the nucleus in the center, and cross striations are present, so those cells are called Tadpole-like cells.
• Myogenin expression is used to distinguish between alveolar and embryonal RMS.
• Chemotherapy combined with three to four drugs (Vincristine, Actinomycin D, and cyclophosphamide. + Irinotecan) + Radiotherapy

Also read: Neuroblastoma -Investigation, Staging and Treatment

Hope you found this blog helpful for your NEET SS Pediatrics Oncology preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.