Frequency and clinical course of residual orbital masses after treatment of orbital rhabdomyosarcoma.

PURPOSE: To evaluate the frequency and clinical course of residual orbital masses on imaging studies after multimodality treatment for orbital rhabdomyosarcoma. DESIGN: Retrospective case series METHODS: : We reviewed records of patients with primary orbital rhabdomyosarcoma who underwent chemotherapy and radiotherapy after surgical biopsy or debulking at 4 US centers during 1998-2019. Demographics, histologic subtype, tumor response 12 weeks after chemotherapy initiation and after completion of all treatment, and imaging findings were analyzed. RESULTS: Thirty-two patients met inclusion criteria. Twenty-two were male, and 30 were younger than 18 years. Histologic subtype was embryonal in 22 patients, alveolar in 8, and mixed embryonal/alveolar in 2. Median follow-up time was 46 months (range, 4.9-199 months). Two patients died. Twenty-seven patients had reliable end-of-treatment imaging findings, of whom 9 had a residual mass. Three residual masses disappeared spontaneously (by 4, 32, and 53 months), 2 remained at last contact, at 2 and 7 years of follow-up, and 3 were excised; 1 progressed and underwent an exenteration. Complete response at 12 weeks was associated with complete response at the end of treatment (p<0.001). Patients with T1 or T2 tumor at presentation were more likely to have complete response at last contact than were those with T3 or T4 tumor (p<0.05). Biopsy type (incisional or excisional) was not associated with response to treatment at any time point. CONCLUSION: A residual orbital mass on imaging may be present after multimodality treatment in approximately one-third of patients. Resolution without biopsy or excision varied from months to years.