Childhood and adolescent cancer survival: A period analysis of data from the Canadian Cancer Registry
Introduction
At just over 160 cases per million, cancer in children and adolescents is rare in Canada—accounting for about 1% of all newly diagnosed neoplasms.1 Nonetheless, cancer is the fourth leading cause of death among Canadians less than 20 years of age, and second only to injuries when the first 28 days of life is excluded.2
Population-based survival studies are essential in evaluating the effectiveness of healthcare provision and the availability of effective treatments for patients with malignant disease.3 While cancer survival among adults in Canada has been well documented,4, 5 estimates of survival among children and adolescents are presently outdated; the most recent figures available were based on cases diagnosed from 1985 to 1988.6 The deficiency of more recent cancer survival data for children and adolescents has led the Canadian Cancer Society/National Cancer Institute of Canada to use the death to case ratio as an indicator of disease prognosis for this population1 and compelled other investigators to draw inferences from survival data from the United States.1, 7 Up-to-date survival estimates for this population are therefore of great interest, especially considering that recent reports from Europe and the United States indicate that the considerable improvement in childhood cancer survival witnessed over the last several decades is ongoing.8, 9 In addition, a new method of survival analysis, known as period analysis, has been introduced to derive more up-to-date estimates of long-term survival than were previously possible using traditional cohort methods.10
The traditional method of estimating cancer survival has been to use a cohort-based method. Only people diagnosed within defined calendar years are included in cohort analyses. Long-term survival estimates derived using the cohort approach pertain to the survival experience of people diagnosed many years ago. Where there has been a subsequent change in prognosis, these estimates will not reflect the long-term survival experience to be expected by newly diagnosed persons.10 Conversely, period analysis results exclusively reflect the survival experience of cases followed up in the most recent period for which data are available; they are, by definition, not based upon a specified diagnostic period. The rationale for this approach is analogous to that of the use of period life tables to estimate current life expectancy.
This paper provides up-to-date estimates of survival for those diagnosed with cancer before age 20 in Canada (excluding Quebec), using period analysis on data from the Canadian Cancer Registry (CCR) as of June 2006. Age-specific survival and survival for different durations of follow-up are presented by diagnostic group and selected subgroups. Five-year period estimates are compared with the latest available estimates based on the traditional cohort method.
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Patients and methods
The CCR is a dynamic, person-oriented, population-based, database maintained by Statistics Canada. It contains cases diagnosed from 1992 onward. The information comprising the CCR is based on reports from every provincial/territorial cancer registry in Canada. However, because data from the province of Quebec are not entirely comparable with those from the other jurisdictions, they were excluded from this report.1, 11 A detailed description of the CCR, including data sources, methodology and
Results
Just over one-quarter of all childhood and adolescent cancer cases diagnosed before the age of 20 in Canada (excluding Quebec) from 1994 to 2003 were leukaemias (Table 1). Three-quarters of the leukaemias, and one-fifth of the overall total number of cases were lymphoid leukaemias. The next most common diagnostic groups during this time period were neoplasms of the central nervous system (19%) and lymphomas and reticuloendothelial neoplasms (16%). The percentage of cases in the remaining
Discussion
Using data from the CCR and the period survival analysis method, the 5-year observed survival estimate for all childhood and adolescent cancers combined in Canada (excluding Quebec) was determined to be 82%. Comparing diagnostic groups, five-year OSPs were highest for retinoblastoma (99%), carcinomas and other malignant epithelial neoplasms and malignant melanomas (91%) and for renal tumours (91%); they were poorest for hepatic tumours (68%) and for malignant bone tumours (68%).
This study
Conflict of interest statement
None declared.
Acknowledgements
The Canadian Cancer Registry is maintained by Statistics Canada. It comprises data supplied by the provincial and territorial cancer registries whose cooperation is gratefully acknowledged.
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