National Registry-based Incidence and Outcome Data on Rhabdomyosarcoma in Australian Children: Stable Incidence, Improving Survival, and High Risk of Second Primary Malignancy

Abstract

Background/Objectives: To describe the incidence and survival of rhabdomyosarcoma in Australia using national data from the Australian Childhood Cancer Registry (ACCR). To investigate second primary malignancy (SPM) in children treated for rhabdomyosarcoma.

Design/Methods: All children (0‐14 years) diagnosed with rhabdomyosarcoma from 1983‐2014 inclusive were identified in the ACCR. Demographic, tumour characteristic, incidence, mortality and treatment data were extracted. Cause‐specific (CS) and event‐free (EFS) survival up to 20 years from diagnosis were estimated using the cohort method. Adjusted excess mortality hazard ratios (HR) were calculated using a multivariate flexible parametric survival model. Cumulative incidence, standardised incidence ratios (SIR), and mortality relating to SPMs were estimated relative to the general population.

Results: There were 600 children diagnosed with rhabdomyosarcoma during the study period. The incidence rate did not change significantly over the study period and was estimated at 4.9 per million children per year between 2010‐2014. CS was 70% and 66% at 5 and 20 years, respectively. Five‐year EFS was 59%. Five‐year CS improved over the study period; from 64% for those diagnosed 1983‐1992 to 75% for 2003‐2012 (p=0.007). Older age at diagnosis (10‐14 years) was associated with poorer survival compared to younger age groups (HR = 1.89 using baseline of 0‐4 years, p=0.001). Of 446 patients achieving remission, 30% relapsed with subsequent 5‐year CS of 34%. The cumulative incidence of SPM at 20 years was 9.9% (n=32). The overall SIR for SPM following rhabdomyosarcoma was 20.8. Girls were 2.6‐fold more likely than boys to be diagnosed with a SPM (p=0.01). Breast cancer accounts for some of the excess female risk. The most common SPMs were thyroid cancer, leukaemias, and osteosarcoma. Mortality was 37% within 5 years of SPM diagnosis.

Conclusions: Five‐year CS for rhabdomyosarcoma has improved over time in Australia. Survivors face a greatly increased risk of SPM and girls are disproportionately affected.