The Ontario Cancer Registry (OCR), operated by Cancer Care Ontario, contains information on all Ontario residents who have been newly diagnosed with all types of malignant cancers, with the exception of basal cell and squamous cell (non-melanoma) skin cancers. The Registry is created using linkages from administrative data, clinical and demographic data from: hospital and regional cancer centre records, pathology reports, and Ontario death certificates. Cancer diagnoses are classified according to the International Classification of Diseases for Oncology, 3rd edition (ICDO-3).
Beginning in 2014, the OCR adopted the National Cancer Institute (NCI) SEER standards for counting multiple primaries for cancer cases diagnosed in 2010 and beyond. This standard is more liberal than the previously used case counting rules from the modified version of the International Association of Cancer Registries (IACR). Cancer incidence data presented on HealthSTATS only includes cases captured using the more conservative IACR definition for all years in order to maintain comparability over time. As a result, figures presented on HealthSTATS may be lower than those reported by Cancer Care Ontario as they are using the revised counting methodology.