Evidence of screening effect derives from descriptive studies of local and national programs in Japan, uncontrolled pilot experiences at a number of sites in Europe and the United States, and population-based studies in Canada and Germany.[1,2,3,4,5,6,7]
An increase in survival rates among screen-detected cases would be expected if screening was detecting neuroblastoma at an earlier and more curable stage. While improved survival rates after initiation of screening have been reported,[8,9] these observations should be viewed cautiously because improvements could be caused by lead-time bias, length bias, and identification of cases through screening that would have spontaneously regressed.
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Screening results in an increased incidence of early-stage disease. The cases detected by screening almost exclusively have biologically favorable properties (unamplified N-myc oncogene, near triploidy, and favorable histology), and this type of favorable neuroblastoma has a high survival rate, whether detected by screening or detected clinically.[1,6,7,10,11,12,13,14,15,16,17] There is evidence that some tumors regress spontaneously in the absence of treatment.[18,19,20,21]
Some authors have argued that the Japanese experience shows that the number of children older than 1 year, who are diagnosed with neuroblastoma, may have decreased since the inception of screening  and that overall mortality has declined during this period.[12,23] A true reduction in neuroblastoma mortality may reflect improvements in treatment efficacy as much as a benefit of treating earlier-stage disease. Mortality has decreased in other countries where screening does not occur. In another study of regional comparisons, disease rates were compared between Osaka, Japan, where screenings were initiated in 1985, and Great Britain, where screening was not done. There was little change during this time in the cumulative mortality rates in either region; 52 versus 57.5 per million between 1970 and 1979 versus 1991 and 1994 in Osaka, compared with 78.6 versus 70.1 in the corresponding periods in Great Britain. In any case, the majority of cases detected by screening at 6 months appear to have biologically favorable prognoses independent of stage.[1,26,27,28,29] Furthermore, despite the shift in stage distribution of cases detected by screening compared with those that are routinely detected, the evidence of reduction in the incidence of advanced-stage cancers in the Japanese experience has been disputed;[3,11,30] in the Quebec Project, as noted below, no such reduction is observed.
A study of mortality trends before and after the national mass screening program in Japan for neuroblastoma analyzed age-specific mortality rates from 1980 through 2006. Screening began in the mid-1980s and was halted in 2003. Mortality rates were either stable through the entire period for age groups 5 years to 9 years and 10 years to 14 years, or were declining before the initiation of screening and continued to do so through 2006 for age groups less than 1 year and 1 year to 4 years. Because the most recent year of death analyzed was 2006, any increase in age-specific mortality associated with the cessation of mass screening in 2003 would have been expected to occur among children aged less than 1 year or 1 year to 4 years. No such increase was observed. This is the first postscreening analysis to provide evidence that screening had no impact on mortality rates and that stopping screening had no adverse effect.