Local therapy is critical in localised pelvic rhabdomyosarcoma: experience of the International Society of Pediatric Oncology Malignant Mesenchymal Tumor (SIOP-MMT) committee.

Background: Localised pelvic rhabdomyosarcomas (pRMS) are rare tumours with a poorer prognosis than the majority of RMS. This study analysed patient outcome according to the type of local therapy delivered and the effect of disease-related factors on prognosis.
Patients and Methods: 97 children with localised pRMS were enrolled in the SIOP-MMT84, 89 and 95 studies. After primary surgery or biopsy, all children received ifosfamide/actinomycin/vincristine-based chemotherapy. Radiotherapy and surgery were planned in patients failing to achieve complete remission.
Results: Median age at diagnosis was 52 months [5 months-18 years]. IRS staging was I for five patients, II for 15 and III for 77. Patients had embryonal RMS (N = 41), alveolar RMS (N = 29), botryoid RMS (N = 3), or not otherwise specified RMS (N = 24).
Outcome: 87 patients achieved local control (90%), 37 relapsed (43%), mainly locally (84%). With a median follow-up of more than 10 years [4-22 years], 5-year OS was 66% (95% CI: 56-75%) and EFS was 52% (95% CI: 42-61%). Among the 18 IRS-I/II patients treated without radiotherapy, 15 survived. Seven out of the 20 IRS-III patients treated without local therapy died. In multivariate analysis, IRS staging, age greater than 10 years and lymph node involvement had a negative impact on OS. Perineal/perianal locations had a trend towards a worse prognosis.
Conclusion: pRMS still have a relatively poor prognosis. Radiotherapy or brachytherapy is necessary for all IRS-III patients including those with radiological complete remission after neoadjuvant chemotherapy with or without surgery. Radiotherapy may be withheld in IRS-I patients and children under 3 years with IRS-II pRMS.
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