Canadians are making progress in the battle against cancer. A new report from Canadian Cancer Society says close to 100,000 lives have been saved over the past 20 years because of the declining rates in cancer deaths.

The biggest factor in the falling death rate is not better treatment and increased cancer survival -- though the last two decades have seen plenty of that, the report says. It's cancer prevention.

That's due in large measure to the fact that falling smoking rates are causing fewer lung cancer cases today, says Gillian Bromfield, the director of Cancer Control Policy at the Canadian Cancer Society.

"One of the biggest reasons we're seeing the decrease in the death rate over the last couple of decades is largely due to the decline in smoking rates in men, which started in the 1960s," Bromfield told CTV's Canada AM Wednesday.

Still, lung cancer remains the leading cause of cancer death in Canada, for both men and women. It takes the lives of more Canadians than breast, prostate and colorectal cancers combined.

Smoking can be blamed for 85 per cent of lung cancer cases, but the habit is also tied to at least 18 other types of cancer, including larynx, oral, stomach, pancreas and kidney.

The report says that lung cancer death rates should continue to fall, since current smoking rates among all Canadians is now 17 per cent, compared to 50 per cent in 1965.

The lung cancer death rate among men has already dropped by 30 per cent between 1988 and 2007. But among women, the death rate has not budged much, though it has now stabilized. That's because smoking rates among women only began to see substantial declines in the 1980s.

The delay means it will be a while before Canadian women see the same type of decline in lung cancer deaths seen among men

Between 1988 and 2007, overall cancer death rates dropped by 21 per cent in men and nine per cent in women. Declines were seen in all the four major cancers that make up more than half of the new cancer cases diagnosed every year in Canada:

  • lung
  • colorectal
  • breast
  • prostate

While the prognosis for many cases of lung cancer is still grim, the good news is that more people are surviving prostate, breast and colorectal cancer.

Breast cancer continues to be the most commonly diagnosed cancer among Canadian women, but the number of new cases each year has been declining. Even better news is that the rate of deaths from breast cancers has dropped even more sharply. It hit a peak in 1986 and has fallen almost 40 per cent since then.

In fact, the report says the breast cancer death rate in Canada is the lowest it has been since 1950, thanks to earlier diagnosis through mammography screening and improved treatments.

Despite all the gains, the Cancer Society says it still has concerns that rising obesity rates may undo some of the progress from falling smoking rates.

"We've seen increases in the incidence of thyroid, liver and kidney cancer, and we're not necessarily sure of all the reasons behind those increases," Bromfield said.

"We think increasing obesity rates may be contributing to kidney cancer, and alcohol use may be driving some of the increase in liver cancer incidence."

An unhealthy diet, a lack of physical inactivity and excess body weight account for a substantial number of cancer diagnoses and deaths each year, the society notes. So too do alcohol consumption, overexposure to the sun and exposure to environmental and workplace carcinogens.

In fact, studies over the last 30 years suggests that about half of cancers can be prevented through changes in lifestyle.

"Even greater gains can be made in reducing cancer rates if more is done to help Canadians embrace healthy lifestyles and if governments do more to create policies that encourage people to make these changes," Bromfield said in a statement.