Rare cancers in Canada, 2006–2016: A population-based surveillance report and comparison of different methods for classifying rare cancers

•There was an annual average of 154,900 cancer diagnoses among Canadians, 2006−2016.•The proportion of rare cancers ranged 9.7–52.5 % using different definitions of rare.•Estimated burden of rare cancers was stable across cancer classification schemes with a lower incidence threshold.•The probability of having a rare cancer was low when cancers were defined by histology vs site.•The effect of sex on probability of having a rare cancer varied by age. The cumulative burden from rare cancers has not been adequately explored in Canada. This analysis aims to characterize the occurrence of rare cancers among Canadians and estimate the probability of being diagnosed with a rare cancer among cancer patients with different demographic characteristics. The Canadian Cancer Registry was used for this analysis. Cancer types were classified in three ways: using the SEER site recode scheme; by histology group; and by site/histology group. The age-standardized incidence rate (ASIR) and 95 % confidence intervals (CI) for each cancer type was estimated for diagnoses from 2006 to 2016. Two ASIR thresholds were used to classify cancers as rare:6/100,000/year and 15/100,000/year. Log-binomial regression was used to estimate the adjusted probability of having a rare cancer among those with cancer by age, sex and geographic region. Using the 6/100,000/year threshold, the incidence proportion (IP) of rare cancers ranged from 9.7 %(95 %CI:9.6,9.7 %)-17.0 %(95 %CI:16.9,17.0 %), and ranged from 19.2 %(95 %CI:19.1,19.3 %)-52.5 %(95 %CI:52.0,53.0 %) using the