The VAC regimen for adult rhabdomyosarcoma: Differences between adolescent/young adult and older patients

Background: Compared to pediatric patients, adult rhabdomyosarcoma (RMS) patients have poor prognoses, but the differences in prognoses and treatment sensitivity between adolescent/young adult (AYA) patient and older RMS patients have not been established.

Aim: To evaluate and compare the efficacy and safety of the vincristine/dactinomycin/cyclophosphamide (VAC) regimen, that is, the standard combination chemotherapy regimen for pediatric RMS, in AYA and older patients.

Methods: We retrospectively reviewed the clinical records of adolescent and adult RMS patients treated at our institution and patients treated with the VAC were enrolled in the analyses. The differences in the efficacy and safety of VAC between the AYA patients (15-39 years old) and older patients (≥40 years old) were compared.

Results: Total of 23 patients were enrolled (14 AYA patients and nine older patients) were enrolled. With the median follow-up of 89.4 weeks (range 17.7-263.1 weeks), the median progression-free survival (PFS) and overall survival (OS) of the VAC regimen were 61.4 weeks (95% CI, 32.6-90.3) and 104.0 weeks (95% CI, 43.8-164.2), respectively, with no significant differences in the PFS or OS between the AYA and older patients. There were no differences in the response rate of the VAC between AYA (64.3%) and older (66.7%), either. Safety profiles were similar between the AYA and older groups, but exposure to antitumor drugs of the VAC tended to be lower in the older group; median number of total cycle of the VAC was 13 in AYA and 10 in older, cumulative cyclophosphamide dose was 16.8 g/m² in AYA and 12.8 g/m² in older, and number of vincristine skips was six in AYA and 12 in older, respectively.

Conclusion: There were no significant differences in responses to the VAC among AYA and older patients with RMS. With the appropriate dose modification, the VAC regimen could be a feasible treatment option for RMS patients >40 years old.