Rhabdomyosarcoma

• Most common pediatric soft-tissue sarcoma
• Aggressive - hematogeneous metastasis, regional LN involvement
  • Most common sites of metastasis: lung, bone marrow
• Derived from embryonic mesenchymal tissue
• Histological subtypes
  • Embryonal - better prognosis, more common in younger children
    • Botryoid variant = "grape-like" appearance
  • Alveolar - poorer prognosis, 80% have PAX-FOXO1 fusion gene
  • Anaplastic/undifferentiated
• Prognosis
  • Poor prognosis: age > 10 years, +PAX/FOXO1 fusion gene
  • Better prognosis: embryonal (esp botryoids) histology, vaginal/paratesticular > bladder/prostate

About 20% GU presentation (majority otherwise in extremities/trunk)

• Bladder, prostate, paratesticular more common
• Gynecological
  • Vaginal/uterine primares a/w good prognosis
  • Presents with mass or bleeding
  • Biopsy, unless can do organ sparing resection
  • 5y OS ~ 5y
• Bladder/prostate
  • Biopsy with TUR, or open transvesical with pelvic/paraaortic LN sampling
  • Residual mass after chemoRT does not always represent viable tumor (e.g. mature rhabdomyoblasts or involuted stroma do not require resection)
    • Mature rhabdomyoblasts -> observation
  • Bladder tumors grown 'within lumen'/remain localized, while prostate often spreads early with large pelvic masses
  • 5y OS ~ 5y
• Paratesticular (7-10%)
  • Generally age 1-5y, arise in distal spermatic cord - unilateral painless swelling/mass distinct from testis
  • Treat with radical inguinal orchiectomy
  • Majority are stage I at diagnosis
  • > 90% are embryonal which is good prognosis
  • Age > 10 years higher risk for RP relapse - get upfront limited nerve-sparing RPLND before chemo for sampling/staging (7-12 nodes) not nodal clearance
    • Age > 10 years regardless of tumor size: nodal involvement ~ 33%
    • Age < 10 years and tumor < 5 cm: nodal involvement ~ 3%
  • If lymph node involvement - radiation
  • Chemo = vincristine + dactinomycin for cN0; + cyclophosphamide for cN1 or M1
  • Surgical management of paratesticular RMS
  • Differential for paratesticular mass (all benign)
    • Adenomatoid tumor of epididymis
    • Leiomyoma
    • Papillary cystadenoma
    • Liopma, angioma, fibroma, dermoid cyst
    • Fibrous pseudotumor

Risk factors

• Advanced maternal age >35 years)
• high birth weight (>4000g) or large for gestational age (>90th percentile)
• maternal drug use
• in utero exposure to radiation

Presentation

• Vaginal - bleeding or introital mass,
• Paratesticular - usually painless scrotal mass
• Bladder and prostate - obstructive symptoms, constipation, urinary frequency, urinary retention, hematuria

Metastatic work-up

• For all patients - CT/MRI including chest; bone scan vs bone marrow biopsy (lung and bone marrow most common sites of metastases)
  • MRI T2 imaging better for evaluating pelvic tumors

Staging:

Multimodal therapy (surgery, chemo, radiation), focus on organ preservation

Surgical resection

• Complete resection only if organ sparing
  • Pretreatment re-excision (PRE) - gross residual tumor that is resectable without organ compromise, microscopically positive margins, or uncertainty of margins
• Otherwise initial surgery = biopsy purposes, and do chemo first
  • Consider delayed primary excision (DPE) (9 wks after chemo) if organ preservation can be achieved after chemo - reduces RT
• If high risk with viable tumor, consider pelvic exent
  • Mature rhabdomyoblasts != viable tumor; can manage with observation
• See first section for organ-specific management

COG grouping:

• Risk based on histology, (embryonal more favorable than alveolar), stage, group
• 5 year survival for embryonal + stage 1/2 ~ 90%, compared to 70% for embryonal stage III, or alveolar. < 30% for stage metastatic disease.