Cancer survival rates higher when detected at earlier stages: StatCan study

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Canadians diagnosed with most common cancers are more likely to survive the disease if they detect it at an earlier stage, according to a new report from Statistics Canada.

The study, released Wednesday, offers the first ever Canadian estimates of five-year cancer survival by stage at diagnosis.

It looked at cases of the most commonly diagnosed cancers in Canada between 2010 and 2017, including lung, breast, prostate, colon and rectal cancer — all of which collectively make up almost half of all diagnosed cancer cases in Canada.

Read more: Cervical cancer rates in Canada and U.S. are dropping. Experts think they know why

The results showed the probability of surviving these cancers decreases if they are diagnosed at a more advanced stage of the disease.

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For example, women diagnosed with breast cancer experienced five-year net survival rates of 100 per cent when the disease was detected in stage I, 92 per cent in stage II, 74 per cent in stage III and 23 per cent in stage IV.

For colon cancer, five-year net survival decreased from 92 per cent at stage I to 11 per cent at stage IV, whereas for prostate cancer, the prognosis was close to 100 per cent for the first three stages, then declined to 41 per cent at stage IV.

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Overall, net survival rates exceeded 90 per cent for all cancers studied that were caught in stage I, except for lung cancer.

For lung cancer, survival rates dropped by just over 20 percentage points between stages I and II of the disease as well as from stage II to III, and decreased by another 13 points from stage III to IV.

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“The work showcases the stage at diagnosis as a key predictor of prognosis and highlights the importance of detecting cancer at an early stage, when treatment is most effective,” the study says.

“The findings can be used by Canadian health professionals to better inform health policy and treatment evaluation.”

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The study did find some exceptions to the overall trend of early diagnosis leading to higher survival rates.

In prostate cancer, the statistics showed survival rates were consistently about 100 per cent for the first three stages of the disease, but declined substantially when diagnosed at stage IV.

Survival rates also did not improve at any stage for colon or rectal cancer cases, according to the data.

Differences in outcomes between men and women were most pronounced for lung cancer, where net survival rates among females exceeded those of males at each stage.

Read more: Cancer survival rates by the numbers in Canada

Age was also an important predictor, as rates of survival of all cancers studied generally decreased the older a patient was, particularly for early-stage lung cancer.

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Between the years 2010 and 2012 and from 2015 to 2017, significant increases in survival rates were observed among stage IV prostate and female breast cancer cases, and among both early- and late-stage lung cancer.

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