beingwell magazine Winter 2008
By: Michael Power

On one hand, it seems, Canadian cancer rates are rising. The word “epidemic” gets bandied about in the media to describe the situation. Some reports say almost one in two people will receive a cancer diagnosis in their lifetime.

Yet, at the same time, we hear death rates are falling and people are living longer after being diagnosed with various forms of the disease.

So, how to make sense of what may seem like conflicting information on
cancer rates? And what can we do to minimize our risk of developing cancer?

How long someone lives after a cancer diagnosis can depend largely on what stage the disease has reached when it’s discovered, said Loraine Marrett, a senior scientist with Cancer Care Ontario.

In general, the earlier a cancer is discovered, the more likely a patient will see favourable outcomes from treatment, Dr. Marrett said.

And, if a screening test is available, we are more likely to be diagnosed before there are even symptoms, she added.

That is the case with, for example, mammographies that look for tumours in the breast or colonoscopies to detect polyps or tumours in the colon. But better testing can lead to temporary spikes in the incidence or detection rate of some cancers because more cases get diagnosed earlier than they would have, had the person waited until symptoms were noted.

“That’s the general pattern,” Dr. Marrett said, “and you see it most dramatically in prostate cancer.”

In the late 1980s, doctors began using a blood test, PSA (prostate specific antigen) to detect early prostate cancer, which led to a rise in the number of diagnosed cases, beginning in 1989. By 1993, the number peaked, then began to decline. Breast cancer follows a similar though less dramatic
pattern.

Another factor contributing to higher survival rates of cancer is better treatment, Dr. Marrett said. For example, while more people are being diagnosed with colorectal cancer (due to better screening), they are living longer with the condition. That’s the result of more effective treatment once it is diagnosed. Similarly, the incidence of breast cancer has been climbing while the life expectancy has been increasing.

With testicular cancer, the incidence has been increasing since statistics started to be recorded, Dr. Marrett said. But mortality from the condition has dropped considerably due to better treatment.

“But we don’t have a good handle on why the incidence (of testicular cancer) has been increasing for some time,” she said. “And we don’t think it’s related to better diagnostic methods.”

The incidence of thyroid cancer has been increasing faster than any other cancer in Canada, possibly because of better investigation of nodules on the thyroid, Dr. Marrett said. Similar to other cancers, mortality for thyroid cancer — which is more common among women than men — isn’t going up.

In fact, the mortality rates for many types of cancer have been dropping, Dr. Marrett said, which is why the rate of diagnosis and the mortality rate aren’t always the same. “It isn’t surprising that they don’t totally agree,” she said.

Not so for all cancers, however. The incidence and mortality rates for lung cancer are similar because people tend to die soon after receiving a diagnosis, Dr. Marrett said. That’s especially true of lung cancer in women, since male smokers began to quit sooner than their female counterparts.

But expect that to change, since women are smoking less, she said. Generally, lower instances of lung cancer follow 10 to 20 years after people begin to butt out in large numbers.

Survival rates for liver cancer have not changed much, although the incidence is increasing, Dr. Marret said.

The number of people in Canada from countries with more prevalence of liver disorders — namely, hepatitis B or C — is increasing, Dr. Marrett said, which could be contributing to the increase. Alcohol consumption is also a contributing factor to liver cancer.

The instance of kidney cancer is higher, too, and the reason may be improved diagnosis along with a higher obesity rate, she said.

As well, melanoma rates are going up. But so are patterns to how people get exposed to the sun. Unprotected recreational exposure such as sunbathing remains common despite warnings regarding the risks to skin health.

So, do all the increasing rates of different cancers represent an epidemic?

“I don’t think there’s good evidence we’ve got an epidemic of cancers,” Dr. Marrett said.
There may be an increase in the number of us receiving a cancer diagnosis, but that doesn’t necessarily mean your chance of getting cancer has increased.

The biggest risk factor for getting cancer is age, and the country’s aging population
contributes to the increase in the number of cases. A growing population also means higher incidence, Dr. Marrett noted. Sure, we hear there are more and more cancer patients to treat, although that doesn’t mean a higher overall incidence.

“It’s context, like everything else.”

As for avoiding cancer, lifestyle choices can play a role, Dr. Marrett said. Quitting smoking can lower your risks of lung cancer considerably. Getting enough exercise and eating well — including not overeating and consuming plenty of fruits and vegetables — also helps lower your risk for several cancers. Avoiding overexposure to the sun also cuts the risk of developing skin cancers.

Although public concern over environmental risk factors remains high, the actual contribution they make to the cancer burden remains small, according to Cancer Care Ontario’s website. A few studies show an increased cancer risk through environmental contaminants such as arsenic, radon, chromium and nitrates. But only a few specific substances, such as radon, solar radiation and second-hand smoke have been well established as carcinogenic.