Paratesticular Rhabdomyosarcoma

Paratesticular rhabdomyosarcoma is a malignant tumour of skeletal muscle lineage arising in the spermatic cord, epididymis or tunica. It makes up about 7 to 12% of childhood rhabdomyosarcomas.

It has a bimodal age peak, in boys aged 1 to 5 years and in adolescents. It usually appears as a painless scrotal mass, and it is curable in most children.

Pathophysiology. The embryonal subtype accounts for most cases (including the favourable spindle cell variant), and the alveolar subtype, with PAX3 or PAX7 fusion with FOXO1, is less common and more aggressive.

Spread is by lymphatics to the retroperitoneal nodes, in about 25 to 40% of adolescents, and by blood to lung, bone and bone marrow.

Staging combines tumour size, nodal status and distant disease with the extent of residual disease after surgery (clinical groups I to IV).

Prognosis is better for age under 10, embryonal histology, localised disease and complete resection. Adults are rarely affected, and the tumour is more aggressive in adults.

A painless, firm, fast growing mass of the scrotum or cord, often thought to be a hydrocele or hernia. The testis can be felt separately in some. Advanced disease causes back or abdominal pain from retroperitoneal nodes, leg swelling and respiratory symptoms.

• Scrotal ultrasound: a solid, hypoechoic, vascular paratesticular mass.
• AFP, beta-hCG and lactate dehydrogenase to exclude germ cell tumour.
• CT or MRI of the abdomen and pelvis and CT of the chest, bone scan or PET-CT, and bone marrow biopsy for staging.
• Histology after radical inguinal orchidectomy, with immunostaining (desmin, myogenin, MyoD1) and PAX-FOXO1 fusion testing for subtype.
• Pre-treatment: full blood count, renal and liver function, audiometry if cisplatin is considered, echocardiography, and fertility counselling.

Differential diagnosis.

• Germ cell tumour of the testis
• Adenomatoid tumour or other benign paratesticular tumour
• Liposarcoma, leiomyosarcoma or fibrous tumour
• Lymphoma and leukaemic infiltration
• Hydrocele, hernia or spermatic cord cyst
• Epididymitis
• Metastasis

• Radical inguinal orchidectomy with high ligation of the cord, with no scrotal incision or biopsy. When the scrotum was violated, perform hemiscrotectomy, and re-excise to obtain clear margins.
• Staging of retroperitoneal nodes: sampling of ipsilateral nodes (nerve sparing) in boys aged 10 years or more, and in younger boys when imaging shows enlarged nodes.
• Chemotherapy within paediatric oncology, by risk group:
  • Low risk (localised, completely resected embryonal tumour): vincristine and dactinomycin for about 24 weeks. Doses: vincristine 1.5 mg/m2 (maximum 2 mg) weekly in the first 12 weeks, and dactinomycin 0.045 mg/kg (maximum 2.5 mg) every 3 weeks.
  • Intermediate risk (nodal disease, residual disease or alveolar histology): vincristine, dactinomycin and cyclophosphamide (1.2 g/m2 with mesna) for about 42 to 45 weeks.
  • Metastatic disease: intensified multi-agent chemotherapy at a specialist centre.
• Radiotherapy: not needed in group I embryonal disease. Microscopic residual disease about 36 Gy, and gross residual or nodal disease about 41 to 50 Gy, to the tumour bed and involved nodes.
• Dactinomycin cautions: extravasation injury, hepatic veno occlusive disease and myelosuppression. Vincristine causes neuropathy and constipation.
• Sperm banking in pubertal boys before chemotherapy. Cyclophosphamide is gonadotoxic, so fertility counselling and testosterone follow up are needed.
• Relapse: salvage regimens at a specialist centre.
• Prognosis: five year survival over 90% in low risk disease, and about 70 to 80% overall for localised disease.

Special groups. Children under 1 year, or under 10 kg, need weight based dosing. Adults need sarcoma centre care.

Monitoring. Imaging of the primary site, retroperitoneum and chest every 3 months for 2 years, then every 6 months for 3 years, then yearly. Hearing, cardiac function, growth and fertility review.

Referral and escalation. Refer to paediatric urology or surgery and paediatric oncology. Urgent referral for any solid paratesticular mass.