The prognosis for many Canadian cancer survivors tends to improve, sometimes substantially, after they survive a year or more, a new Statistics Canada report suggests.
For the first time, Statistics Canada has estimated survival rates for people who have already lived at least a year with cancer. The risk of death is often greatest in the first year, the agency said, and old prognosis estimates for the years that follow may no longer apply.
"The good news in this story is, for many, many patients, once they have gone for two or three or four years after cancer diagnosis, their survival compared with the general population is really dramatically better than it was at that time they first had that chat with their oncologist," said Dr. Heather Bryant, a co-author of the report and vice-president of cancer control for the Canadian Partnership Against Cancer.
The researchers analyzed data involving patients across the country and 26 different kinds of cancer diagnosed between 2004 and 2006, looking at survival rates at different time periods after diagnosis. The estimates are based on the average survival time for large groups of patients, rather than an individual's prognosis.
The researchers gathered conditional survival data, which means they compared the survival rates of cancer patients at different periods after diagnosis with survival rates of people in the general population who don't have cancer.
"Conditional survival data provide more accurate prognostic information about how the risk of death changes over time," the report's authors said.
"These results could assist people who have survived one or more years after a cancer diagnosis in adjusting their view of the future, and help cancer-care providers in planning followup."
Early detection for colorectal cancer
The estimated five-year survival rate for people with cancer of the pancreas is six per cent at diagnosis, but it's 28 per cent among one-year survivors and 88 per cent among five-year survivors.
Similarly, among those surviving esophageal cancer for at least five years, the estimated survival rate is 83 per cent, although the initial prognosis is 13 per cent.
For five-year survivors of colon cancer, a cancer with an initial estimated five-year survival rate of 63 per cent, the updated prognosis is 97 per cent, the authors said.
The findings also have implications for cancer control, Bryant said.
For a cancer like colorectal cancer, where the initial prognosis is poor, health-care providers would want to concentrate improving early detection to improve survival chances.
But with a cancer such as breast cancer, where the five-year survival rate is fairly high, the focus should be on helping patients beyond those first five years.
"If the patient lives five years, what's her chance of living five more or even 10 more years, because that's where the differences are going to be made," Bryant said.
One surprise in the study, she said, was that there was no apparent improvement in survival prospects during the first five years after diagnosis for chronic lymphocytic leukemia or CLL, with an estimated five-year relative survival ratio remaining at just under 80 per cent.
In the case of CLL, the findings suggest doctors and researchers shouldn't focus all of their attention on five-year survival rates, since they are fairly stable, but look for ways to prevent later recurrence of the disease.
The national study gave researchers a chance to look at smaller, rarer cancers and tease out some differences that fit with clinical understanding of those diseases, Bryant said.
Epidemiologist Prithwish De of the Canadian Cancer Society said treatments might explain part of the results in terms of improved survival over time, but added more research needs to be done to find out what role treatment actually plays compared with other factors that affect survival.
The group is working on building stage-specific survival cancer information for four major cancers — breast, colorectal, lung and prostate — since the chances of surviving for five years differs depending on the stage when it is diagnosed.