Case-Completeness of Nonmalignant Central Nervous System Tumors in the Canadian Cancer Registry, 2011-2015

Introduction: The public health burden of nonmalignant central nervous system tumors (NMCNSTs) in Canada is unclear because casefinding and registration have historically been incomplete. The primary objective of this study is to quantify case-completeness of NMCNSTs in the Canadian Cancer Registry (CCR) using US Surveillance, Epidemiology and End Results Program (SEER) rates as the standard.

Methods: Counts, distributions, and age-standardized incidence rates (ASIRs) for malignant central nervous system tumors (MCNSTs) and NMCNSTs by sex, age, site, histology, tumor size, World Health Organization (WHO) grade, and year of diagnosis were estimated for the United States and Canada (excluding Quebec) for the time period 2011-2015 using SEER and CCR data, respectively. Canadian and provincial standardized incidence ratios (SIRs) were also calculated by sex, age, site, histology and year of diagnosis using SEER rates as the standard. Under the assumptions of high NMCNST case-completeness in SEER registries and comparable population-based rates in the United States and Canada, SIRs less than 100% suggest incomplete case registration.

Results: Between 2011 and 2015, the ASIR for MCNSTs is similar in the United States (6.97 per 100,000 persons; 95% CI, 6.89-7.05), Canada (7.11 per 100,000; 95% CI, 6.97-7.24), and across provinces (range, 6.53-7.35 per 100,000). Conversely, the ASIR for NMCNSTs is 1.61 times greater in the United States (17.15 per 100,000; 95% CI, 17.02-17.27) than Canada (10.65 per 100,000; 95% CI, 10.49-10.82). SIRs for NMCNSTs range from 22.5% (95% CI, 15.6%-31.5%) in Prince Edward Island to 85.3% (95% CI, 83.7%-86.9%) in Ontario and vary by demographics, tumor characteristics, and year. Identified data limitations include nonspecific tumor characteristics and potential misclassification.

Conclusion: NMCNST surveillance in Canada is compromised by incomplete case registration and data quality limitations. Enhancement of case ascertainment processes for these tumors, which may be diagnosed radiologically, may be warranted.