TORONTO - While more people are being diagnosed with cancer due in part to the aging population, more are also surviving the disease for longer and altering the picture of cancer in Canada, a Statistics Canada study suggests.
The study, released Wednesday, shows the five-year prevalence rate for cancer rose by 2.1 per cent a year between 1997 and 2008.
That prevalence rate is a measure of how many people have been diagnosed with various types of cancer in the previous five years and are still alive in a particular year. Prevalence is different from incidence, a term which refers to newly diagnosed cases.
For all cancers combined, the five-year prevalence rate at the beginning of 2008 was 1,490 cases for every 100,000 people — meaning that about half a million Canadians are cancer survivors.
"I think over the past few decades ... cancer is becoming increasingly de-stigmatized and it's interesting to see how many people in the population have been diagnosed with cancer, and that figure continues to increase," said Kathryn Wilkins, a senior analyst with Statistics Canada who co-authored the report.
One reason for the higher prevalence rates is the greying of Canada's population: many cancers tend to develop as people reach older age, Wilkins said from Ottawa.
"We found that for all cancers combined, the aging of the population accounts for about half the rise in the rate of prevalence."
Still, increases in prevalence also mean more Canadians are living longer after a cancer diagnosis, she said, noting that more widespread screening leading to diagnosis often means a better chance for earlier treatment and a better outcome.
The study found the increases in prevalence were most pronounced for liver and thyroid cancers, while the rates declined for cancers of the larynx and cervix.
The rate for prostate cancer, the most commonly diagnosed cancer in Canada, rose three per cent a year over the 11-year study period. Over the same time, the rate for breast cancer went up an average of 1.3 per cent a year.
"The rise for breast cancer was marginal and almost all due to the aging of the population," said Wilkins.
Prithwish De, an epidemiologist at the Canadian Cancer Society, said the study is valuable because it's the first time the federal agency has looked at the change in cancer prevalence over a span of time.
"And this is important because it gives us a sense of how big the cancer survivor population currently is and changing over time," said De, explaining that the health-care system needs to be ready to care for the growing number of Canadians living with cancer or following treatment.
For most people, cancer-care services required within the first five years after diagnosis include primary treatment and supportive care, followed by close monitoring for recurrence.
Dr. Ralph Meyer, a professor of oncology at Queen's University, said a higher number of cancer cases related to the aging population plus increased numbers of survivors will translate into a greater burden on the health-care system.
"Some of the successful treatments that are increasing the ability to live with the disease and thus affect the prevalence relate to new (drug) therapies that happen to be quite expensive," Meyer said from Kingston, Ont. "So the requirement of the health-care system to look after, to provide for cancer patients, the volume and the complexity has increased substantially because of an aging population and new therapies."
Survivors are a "kind of new subpopulation of patients who are now in a different circumstance than was seen before," he said. "And there are new demands on following the patients and trying to improve their quality of life after going through cancer and the sequelae (aftereffects) that relate both to the disease and its treatment."
De of the Cancer Society said the study will help health-care policy makers and cancer-care and prevention organizations better target resources.
"The report certainly identifies those cancers where we need to pay more attention to in terms of making sure that we try to reduce their incidence, and for those who are afflicted by those specific cancers, that we have the necessary resources to be able to care for cancer survivors after their treatment."
One of those could be lung cancer. Its prevalence rose by an average of 1.3 per cent a year, but diverged sharply between men and women, the study found. In men, the rate declined 0.3 per cent a year, while in women it increased 3.0 per cent a year.
The study suggests the difference is due to a greater drop in smoking rates among men in the late 1960s.
"The difference between men and women in lung cancer is to be expected," said Wilkins. "It's kind of alarming to see that the (prevalence) rates haven't started to go down yet for women."