Shorter-duration therapy with vincristine, dactinomycin and lower-dose cyclophosphamide with radiation therapy did not compromise failure-free survival in patients with low-risk embryonal rhabdomyosarcoma, according to results of a noninferiority trial.
Prior studies showed treatment with vincristine, dactinomycin and cyclophosphamide (VAC) improved failure-free survival in patients with subset-one low-risk embryonal rhabdomyosarcoma.
In the current study, researchers assessed whether vincristine, dactinomycin and lower-dose cyclophosphamide (total cumulative cyclophosphamide dose, 4.8 g/m2) plus radiotherapy would compromise failure-free survival compared with the established regimen, which includes a total cumulative cyclophosphamide dose of 26.4 g/m2.
The analysis included 271 patients with newly diagnosed subset-one embryonal rhabdomyosarcoma. The most common primary sites were paratestis (n=118; 44%) and orbit (n=82; 30%).
Patients received four cycles of VAC, followed by four cycles of vincristine and dactinomycin over a 22 weeks.
Researchers observed 35 failures in the study population, compared with 48.4 failures expected based on a trial of the longer-duration regimen in a similar patient population.
Overall, researchers estimated 3-year failure-free survival of 89% (95% CI, 85% to 92%) and 3-year OS of 98% (95% CI, 95% to 99%).
Patients with paratesticular patients achieved the most favorable outcomes. In that group, 3-year failure-free survival was 93% (95% CI, 87-96) and 3-year OS was 99% (95% CI, 94-99). Among patients with orbit tumors, 3-year failure-free survival was 86% (95% CI, 77-92) and 3-year OS was 97% (95% CI, 90-99).
Cumulative failure rates at 3 years were as follows: local failure, 7.6%; regional failure, 1.5%; and distant failure, 3.4%. No unexpected grade 4 toxicities developed, and no toxicity-related deaths occurred.
The survival outcomes and the lack of increased toxicity suggest the shorter-duration regimen may be suitable for patients with low-risk embryonal rhabdomyosarcoma, the researchers concluded.
“Identification of biologic features or biomarkers associated with treatment failure will be important for future novel therapeutic approaches or additional changes in treatment strategy,” they wrote.
Disclosure: The researchers report no relevant financial disclosures.