Long-term cause-specific mortality among five-year survivors of childhood cancer

Background: The purpose of our study was to assess long-term cause-specific mortality of 5-year childhood cancer survivors.

Procedure: The study population consisted of 1,378 patients who had been treated for childhood cancer in The Netherlands between 1966 and 1996 and survived at least 5 years; follow-up was complete for 99% of survivors. Cause-specific mortality was compared with general population rates to assess relative and absolute excess risks of death (standardized mortality ratio (SMR) and AER).

Results: After a median follow-up of 16.1 years, 120 patients had died. The overall SMR was 17-fold (95% CI: 14.3-20.6) increased compared to the general population. Our cohort experienced an excess of 7 deaths per 1,000 person-years. Patients who received combined modality treatment and were treated for at least one recurrence experienced the highest risk of death (SMR = 92.3; AER = 37.0 per 1,000 person-years). The SMR appeared to stabilize at an about 4 to 5-fold increased risk of death after 20 years of follow-up. Only after more than 20 years of follow-up excess mortality due to other causes than the primary cancer exceeded mortality from the primary childhood cancer (2.3 vs. 0.3/1,000 patients/year). The SMR for all causes other than primary cancer was 5.4 in 25-year survivors. The overall risks of death strongly decreased with increasing attained age, with an SMR of 1.6 (n.s.) and an AER of 0.3 per 1,000 person-years for survivors of 30 years or older.

Conclusions: The first primary cancer contributes most to the absolute excess risk of death in 5-year survivors of childhood cancer, but after 25 years childhood cancer mortality is negligible. Relative risk of death due to other causes is still significantly increased after 25 years of follow-up.