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How We Collect Cancer Registry Data

The Ontario Cancer Registry is the provincial database of information for all Ontario residents who have been newly diagnosed with cancer (except for basal cell carcinoma and squamous cell carcinoma of the skin) or who have died of cancer. The registry is a passive registry that collects data from hospitals, regional cancer centres, pathology reports and death certificates. The registry also captures data on cancer staging for some cancer types and enables integrated linking with other data, such as treatment data.

Rules Used for Capturing Cancer Cases

The Ontario Cancer Registry registers newly-diagnosed cases of invasive cancers according to current Canadian and U.S. standards, beginning with cases diagnosed in 2010 and beyond. It conforms to specific standards set out by the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) multiple primary and histology coding rules for counting additional primary cancers. 

For international reporting of cancer incidence, the Ontario Cancer Registry will continue to use reporting standards set out by the World Health Organization’s International Agency for Research on Cancer (IARC) to align with reporting by countries outside of North America.

How the Current Registry Differs from the Decommissioned Registry

Cancer Care Ontario’s first electronic cancer registry (the Ontario Cancer Registry Information System (OCRIS)) was formally decommissioned on October 29, 2014 and replaced with the current Ontario Cancer Registry. The current registry uses new technology and advanced standards for counting cancer cases.  

The Ontario Cancer Registry’s adoption of the National Cancer Institute’s SEER standards increases the incidence number of certain types of cancer reported in Ontario. However, this change in number is due to how cancers are being counted; it does not mean that more people in Ontario are being diagnosed with or dying of cancer.

The OCRIS rules for counting multiple primary cancers were conservative compared with the SEER rules currently used in the Ontario Cancer Registry. OCRIS rules were based on IARC rules, modified to handle the types of cancer notifications that Cancer Care Ontario received when the system was built in the early 1980s. 

The OCRIS did not recognize paired organs (e.g., left or right breast) or subsites (e.g., colon and skin melanoma). It also did not have timing rules for subsequent new primary cancers in the same organ, counting only 1 cancer type in an organ. Additionally, the OCRIS had several specific algorithms that disqualified information deemed to be possible reports of metastatic disease or relapse. These rules resulted in even fewer primaries than produced by the IARC rules. 

By contrast, the current Ontario Cancer Registry counts paired organs and multiple cancers in 1 organ. There are 11 rule sets in all, each having specific multiplicity rules.

For example, it will count:  

  • left and right breast cancers
  • a new primary cancer in the same organ after specified time frames
  • melanomas of the arm, leg or trunk as separate primary cancers
  • ductal carcinoma and then a sarcoma of the same breast as two primary cancers


Working with Data from the OCRIS

The Ontario Cancer Registry applies specific SEER standards from 2010 and later. Historic cases from the OCRIS (1964 to 2009) have been imported into the Ontario Cancer Registry to allow for continued use for analytic purposes. If a report spans the cut-over from the OCRIS to the registry cases, special care must be taken to reconcile the different data sets. For comparison purposes, data from 2010 and beyond must be converted using the International Agency for Research on Cancer (IARC) rules to ensure equivalent comparison with data from 2009 and earlier. The registry database provides an IARC flag field to facilitate this.