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4 Multidisciplinary Management of Orbital Rhabdomyosarcoma

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therapy. In patients with ARMS, a more aggressive subtype, radiation therapy is always recommended regardless of surgical margin status.

4.5 Chemotherapy

All RMS cases require chemotherapy, and the standard chemotherapeutic regimen is a three-drug combination of vincristine, dactinomycin, and cyclophosphamide. The IRS-II study demonstrated an excellent outcome for patients treated with this regimen: the overall survival rate at 5 years was 92% [16]. Thus, the next two clinical trials of the IRSG, IRS-III and IRS-IV, examined the effect of decreasing the amount of chemotherapy given to patients with orbital RMS, especially those with clinical group I or II disease. The strategy was to exclude cyclophosphamide since it has been associated with late effects such as infertility, secondary malignancies, and osteoporosis [16, 17]. In IRS-III and IRS-IV, patients with group I or II disease received only vincristine and dactinomycin; the main difference between the trials was that in IRS-IV, the duration of therapy was shortened from 50 to 36 weeks [5, 14]. The results were similar to those of IRS-II: the 3-year failure-free and overall survival rates were 91 and 100%, respectively, for IRS-IV with IRS-III having similar results.

Most orbital RMS patients have clinical group III disease. In IRS-III, patients with group III disease received only vincristine and dactinomycin, but in IRSIV, patients with group III disease received the three-drug regimen. The 3-year failure-free survival rate was significantly better with the three-drug combination (94 versus 80%), but overall survival was not significantly different [13, 17]. In the most recently completed IRSG trial, IRS-V, the two-drug strategy was used: patients with group I, II, or III orbital RMS were treated with a 45-week regimen of vincristine with dactinomycin. The results of the IRS-V trial have not yet been published. The current Children’s Oncology Group study for patients with low-risk RMS is attempting to determine if 22 weeks of treatment with vincristine, dactinomycin, and cyclophosphamide is feasible. Only four doses of cyclophosphamide are given, and the dose is 1.2 g/m2 rather than the 2.2-g/m2 dose used in prior trials.

4.6 Radiation Therapy

Radiation therapy is a key component in the treatment of RMS. Earlier IRSG studies demonstrated good local control rates with doses of 50.4 Gy. However, the potential late side effects of radiation therapy in orbital RMS survivors need to be recognized. One study of 94 orbital RMS survivors noted that 82% of the patients had a unilateral cataract and 59% of the patients had orbital hypoplasia due to delayed bone growth [18]. Other described effects include dry eye, keratitis, and hormone insufficiency [18, 19]. Thus, there has been great interest in reducing the delivered radiation dose while maintaining the excellent cure rate for orbital RMS. The

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recently completed IRS-V study and the current Children’s Oncology Group study for patients with low-risk RMS employ a strategy in which the dose is dependent upon clinical group and nodal status. Group I patients do not receive radiation therapy. Group II patients receive 36 Gy if there are no clinically involved nodes and 41.4 Gy if there are proven clinically involved lymph nodes. Group III patients, who account for the vast majority of patients with orbital RMS, receive 45 Gy.

Currently, most patients are treated using external-beam photons; however, there has recently been interest in other modalities, such as proton beam therapy, which have the theoretical advantage of an improved dose distribution with greater sparing of surrounding normal tissues [20]. Orbital tumors may be an excellent indication for proton therapy because of the reduced dose to the surrounding brain, neuroendocrine structures, and contralateral eye. Although there are some early data indicating safety and feasibility of proton therapy for orbital RMS in pediatric patients, there are scant long-term data regarding local control and the rate of late effects [21].

4.7 Conclusions and Future Directions

The survival outcome for orbital RMS has improved significantly over the years because of advances in multidisciplinary care. However, long-term survivors of orbital RMS are now experiencing a new set of challenges in terms of late-onset side effects as a result of their cancer therapy. Improvements in all facets of care must continue to be attempted in an effort to lessen the long-term effects of therapy while maintaining the rate of cure.

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