What is New in Rhabdomyosarcoma Management in Children?

Abstract

Optimal management of rhabdomyosarcoma requires establishing the correct pathologic diagnosis, histologic sub-type, primary site, extent of disease (Stage), and extent of resection (Group). Based on these features, cooperative groups in North America and Europe have defined risk-adapted treatments that include surgery, chemotherapy, and usually radiotherapy. This article focuses on recent findings that can impact or have already impacted rhabdomyosarcoma treatment guidelines and highlights controversies that should be addressed in order to improve outcome for children with rhabdomyosarcoma. Rhabdomyosarcoma is currently sub-classified in children based on histology into the favorable embryonal/botryoid/spindle cell types and the unfavorable alveolar form. Risk group assignment depends in part on histologic sub-type. Alveolar rhabdomyosarcoma is sometimes associated with chromosomal translocations, which impact clinical behavior. An important ongoing debate is whether molecular diagnostic tools to identify chromosomal translocations and/or define gene expression profiles should be used to sub-classify rhabdomyosarcoma rather than histology. Clinical trials continue to evaluate retrospective as well as prospective cohorts in order to carefully determine the impact of histology versus biologic features on outcome in the context of specific therapeutic regimens. Most rhabdomyosarcoma recurrences involve the primary site or adjacent region. Cooperative groups continue to investigate new approaches to local control in order to reduce local recurrences and sequelae associated with local therapy. Delaying primary resection until after chemotherapy has started appears to increase the number of tumors that can be completely resected with acceptable morbidity in some primary sites. Radiation dose reductions following delayed primary resection have been investigated. Although outcomes appear similar to the conventional approach of full-dose radiotherapy without delayed primary resection, long-term effects of the two approaches have not been rigorously compared. Early evidence suggests that newer methods of delivering radiotherapy, including intensity-modulated radiotherapy (IMRT), proton beam radiotherapy, and brachytherapy maintain efficacy but may reduce long-term sequelae compared with 3-dimensional conformal radiotherapy. Chemotherapy regimens defined by the cooperative groups vary by risk group. The most commonly used regimens include vincristine and dactinomycin in combination with an alkylating agent, either cyclophosphamide or ifosfamide. In order to improve outcomes, recent clinical trials have introduced new chemotherapeutic agents (e.g. topotecan, carboplatin, or epirubicin) into the treatment regimens. However, outcomes have not been significantly impacted. Novel chemotherapy administration schedules have been tested in patients with metastatic rhabdomyosarcoma, including interval compressed dosing or maintenance therapy, and may be promising. Molecularly targeted agents are currently under investigation in combination with chemotherapy for patients with recurrent or metastatic rhabdomyosarcoma. It is hoped that these novel agents will benefit all patients with rhabdomyosarcoma in the future.