The impact of incomplete registration on survival rate of children with very rare tumors

Abstract

Background. Pediatric very rare tumors (VRTs) represent a heterogeneous subset of childhood cancers, with reliable survival estimates depending dramatically on each (un)registered case. The current study aimed to evaluate the number of VRTs among Lithuanian children, to assess the impact of the registration status on survival rate and to track changes in treatment outcome over the 16-year study period. Methods. We performed a population-based retrospective study across children below 18 years old diagnosed with a VRT in Lithuania between the years 2000 and 2015. The identified cases were cross-checked with the Lithuanian Cancer Registry – a population-based epidemiology cancer registry – for the fact of registration and survival status. The overall survival was calculated according to the registration status and treatment period. Results. Thirty-seven children with VRTs were identified within the defined time frame. Six of them (16.2%) were not reported to the Lithuanian Cancer Registry at diagnosis. The probability of overall survival at 5 years (OS5y) differed significantly between the registered (n = 31) and unregistered (n = 6) cohorts: 51.6% vs 100%, respectively (p = 0.049). A 5-year survival estimate for children diagnosed with a VRT at the age of 0-14 years differed by 10% according to the registration completeness: 52.1% calculated for the entire cohort vs 42.1% for registered patients only. The OS5y did not improve over the analyzed period: 61.1% in 2000-2007 vs 57.9% in 2008-2015 (p = 0.805). The survival continued to decline beyond 5 years due to late cancer-related adverse events: 59.5% of patients were alive at 5 years as compared to 44.3% at 10 years. Conclusions. The OS5y of children affected by VRT was lower than in more common childhood cancers. The survival rate of the unregistered patients was superior that mislead interpretation of treatment outcome. Meticulous registration of VRTs is crucial for correct evaluation of treatment outcome, especially across small countries with few cases.