Vincristine (V), dactinomycin (A), and lower doses of cyclophosphamide (C) with or without radiation therapy for patients with newly diagnosed low-risk embryonal rhabdomyosarcoma (ERMS): A report from the Children’s Oncology Group (COG).
9509 Background: Intergroup Rhabdomyosarcoma Study (IRS) trials showed improved survival with VAC compared with VA for patients with Stage 1 Group III (non-orbit) or Stage 3 Group I/II ERMS (see table). In COG ARST0331, we hypothesized that VA in combination with lower doses of C (total cumulative dose=4.8 g/m2) would produce the benefit of IRS-IV VAC with less toxicity for patients with Stage 1 Group III (non-orbit) or Stage 3 Group I/II low-risk ERMS. Methods: This single arm, non-inferiority, phase III study enrolled newly diagnosed patients with Stage 1 Group III (non-orbit) ERMS or Stage 3 Group I/II ERMS onto Subset 2. Therapy was 4 cycles of VAC followed by 12 cycles of VA over 46 weeks (total cumulative doses: V=54 mg/m2, A=21.6 mg/m2, C=4.8 g/m2). The radiation therapy dose was 36 Gy for Group IIA patients, 41.4 Gy for Group IIB/C patients, and 50.4 Gy for Group III patients. From 2004–2008 girls with Group III vaginal RMS did not receive radiotherapy if a complete response was achieved with chemotherapy with or without delayed resection. The primary endpoint was failure-free survival (FFS), and results were compared with a fixed expected outcome. Results: With a median follow-up of 3.0 yrs, we observed 16 failures vs. 7.8 expected failures. Estimated 3-yr FFS was 63% (95% CI: 46%, 75%) (n=60), and overall survival (OS) was 84% (95% CI: 68%, 93%). Estimated 3-yr FFS was 46% (95% CI: 23%, 67%) for girls with non-bladder genitourinary tract ERMS (n=21) and 75% (95% CI: 53%, 88%) for all other Subset 2 patients (n=39). Conclusions: We observed suboptimal FFS of patients with Subset 2 low-risk RMS using reduced total cyclophosphamide (4.8 g/m2). Results were complicated by the choice of no radiation therapy for girls with vaginal tumors. Future studies for low-risk RMS Subset 2 patients could investigate a dose of C between 4.8 and 26.4 g/m2 with VA and local radiotherapy. [Table: see text]