With roughly 250 new cases each year, pediatric rhabdomyosarcoma (RMS) makes up slightly less than one half of all pediatric soft tissue sarcomas diagnosed within the United States .
Sites of origin are varied and tumors can arise anywhere within the body. Common sites include the head and neck (35%), genitourinary tract (24%), extremities (19%), and elsewhere (22%) .
- Treatment for RMS depends on risk group stratification. The intensity of chemotherapy and the use of surgery and/or radiotherapy vary between high-, intermediate-, and low-risk groups, which are determined by primary site, stage, clinical group, and histology.
- Primary Site: The primary sites of origin are categorized as favorable or unfavorable:
Favorable sites include the orbit, head and neck, genitourinary tract, and biliary tract.
Unfavorable sites include bladder, prostate, perineal/perianal and retroperitoneum, trunk and extremity, and parameningeal tumors.
Tumors that involve two adjacent sites with differing designations of favorability are classified as “unfavorable,” so as not to risk delivering inadequate treatment.
Stage: The staging for pediatric RMS utilizes the tumor, node, and metastasis (TNM) system but also takes into consideration the primary site (Table 8.1).
Clinical Group: The postsurgical extent of disease at the time of chemotherapy initiation determines the clinical group in RMS. The group designation represents the tumor extent before any chemotherapy has been given, and children who have a delayed surgical resection after chemotherapy has begun are still classified based on their initial pre-chemotherapy designation (Table 8.2).
Histology: RMS is segregated into favorable (embryonal, botryoid, and spindle cell) and unfavorable (alveolar) histologic subtypes. Embryonal histology comprises 60–70% of all cases, and alveolar histology is seen in 20% of cases . Two translocations, PAX3-FOXO1 and PAX7-FOXO1, involving the transcription factor FOXO1 define alveolar genetics. The presence of these translocations portends a worse prognosis, whereas the absence of these translocations in histologically alveolar tumors indicates an outcome similar to embryonal tumors. In the current COG study, ARST1431, FOXO1 positivity is used to determine risk group and dose .
- Risk Group: Currently, the RMS risk stratifications used by the Children’s Oncology Group (COG) studies separate children into three risk groups (low, intermediate, and high risk). Overall survival varies between the groups and is roughly 98% for low-risk patients, 78% for intermediate-risk patients, and 30% for high-risk patients [5–7]. The current designations for each group are as follows:
Low risk: Low-risk RMS is defined as nonmetastatic embryonal RMS arising in favorable sites (stage 1) with any clinical group (group I–III) or embryonal RMS arising in unfavorable sites with either completely resected disease (group I) or microscopic residual disease (group II)
Intermediate risk: Intermediate-risk RMS is defined as nonmetastatic (group I–III) alveolar RMS arising at any site (stage 1–3) or incompletely excised (group III) embryonal RMS arising in an unfavorable site (stages 2 and 3).
High risk: Patients with metastatic RMS (group IV, stage 4)
- 5.Arndt CA, Stoner JA, Hawkins DS et al (2009) Vincristine, actinomycin, and cyclophosphamide compared with vincristine, actinomycin, and cyclophosphamide alternating with vincristine, topotecan, and cyclophosphamide for intermediate-risk rhabdomyosarcoma: children’s oncology group study D9803. J Clin Oncol 27:5182–5188CrossRefGoogle Scholar
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