Healthy Canadians; 46-49 HTL Five-year relative survival rate

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Definition

The ratio of the observed survival for a group of cancer patients five years after diagnosis to the survival that would have been expected for members of the general population assumed to be practically free of that cancer and who have the same main characteristics associated with survival (such as sex, age, area of residence) as the cancer patients.

Rationale and Notes for Interpretation

Relative survival is the most widely used method for analyzing the survival of cancer patients in population studies. It provides an objective measure of the proportion of patients dying from the direct or indirect consequences of their disease in a given population. That is, a measure of patient survival corrected for the effect of other independent causes of death.

Age standardized relative survival ratios are interpretable as the relative survival ratio that would have occurred if the age distribution of the patient group under study had been the same as that of the standard population. Age standardization controls for a bias that may be introduced by comparing relative survival estimates amongst provinces with different case age distributions. Unless they have been age-standardized to the same population, relative survival ratios from other sources should not be compared with those presented in this analysis.

The relative survival rate is influenced by two distinct groups of factors: (1) the severity (stage) of the cancer at the time of diagnosis, and (2) the effectiveness of cancer treatment after diagnosis. While the indicator does not shed light on the relative importance of these two kinds of factors, from the viewpoint of interpreting the indicator, these two factors work in the same direction. For example, an improvement in screening would result in cancers being detected at an earlier stage, where treatments are generally more successful, resulting in better observed survival. And if there had not been a significant change in screening, better observed survival would indicate more effective and successful cancer treatment after diagnosis. This interpretation issue is currently being addressed by the addition of staging data to the cancer registry systems. Cancer staging data indicates how advanced (serious) the cancer is at the time of diagnosis.

Prostate, breast, lung and colorectal cancer are reported on because they represent the four most common cancer sites. In particular, lung cancer relative survival rates are reported to inform the public of the poor prognosis of this cancer. The fact that health system interventions with lung cancer are not very successful underscores the need to emphasize preventive strategies.

It should be noted that variations in the use of prostate cancer screening (prostate specific antigen or PSA testing) have affected incidence rates of prostate cancer over the past ten years, and this has likely had an impact on relative survival ratios.

Technical Specifications

Exclusions: Restricted to the first primary cancer diagnosed for an individual. Subjects with an unknown year of birth or death; subjects younger than 15 or older than 99 years of age at diagnosis; subjects diagnosed through autopsy or death certificate only were excluded. Cases diagnosed in Quebec were not included (..) in the national estimates of five-year relative survival partly because the method of ascertaining the date of diagnosis in this province clearly differed from that of the other provincial cancer registries.

Source: Statistics Canada , Canadian Cancer Registry, Canadian National Mortality Data Base, and Canadian and provincial life tables (1990-1992, 1995-1997); ISQ

Data Availability

Colorectal and lung cancer relative survival ratios are reported for each sex separately and for both sexes; prostate cancer survival is reported for males and breast cancer survival for females.

Results from the most recent data available (i.e. based on cases diagnosed between 1992 to 1997) are reported for all provinces except Quebec . Results for the territories are not reported separately because of an insufficient number of cases for analysis. Cases from these areas are, however, included in the national estimates.

Age-standardized rates are available.

Considerations for Indicator Quality and Comparability

Comparison with the Canadian age-standardized ratio is recommended.
National and provincial results should be reported in a table.
95% confidence intervals should be reported with each estimate.

Number of eligible cases and number of deaths in the first five years of follow-up may also be reported. Analysis was conducted using the life-table method; expected survival proportions were derived using the Ederer II approach. Relative survival ratios were standardized to the age distribution of eligible patients diagnosed with the specific cancer from 1992 to 2001. Confidence intervals were formed from standard errors estimated using Greenwood ’s method. National estimates exclude Quebec.

Cases diagnosed in Quebec were not included (..) in the national estimates of five-year relative survival partly because the method of ascertaining the date of diagnosis in this province clearly differed from that of the other provincial cancer registries.