Understanding the Drop in Cancer Cases

Doctors say the downturn is good news, but the reasons behind it are unclear.

Nov. 25, 2008— -- For Sarah Theresa Gonzales of Bronx, N.Y., her cousin's death last year from lung cancer was a wake-up call.

"I was fearful that I was going to get cancer," Gonzales, 55, said. "I think it was this anxiety that got to me. I just grabbed my cigarettes, grabbed my lighter, grabbed everything and dumped it down the incinerator."

Gonzales had smoked for 31 years. She decided to quit June 15, after logging on to the "cold turkey" quitting-forum-cum-support-group WhyQuit.com. She has not taken a puff since.

In the past decade, the fear of cancer has driven Gonzales and millions of other Americans to kick the smoking habit -- a fact that some doctors say could be a major contributor to an overall down-tick in cancer incidence reported today in the Journal of the National Cancer Institute.

Looking at the 15 most common cancers found in men and women, researchers found that the overall cancer rate has dropped 0.8 percent per year from 1999 to 2005.

Never before in the history of the annual study -- a collaboration between the American Cancer Society, the Centers for Disease Control and Prevention, the National Cancer Institute and the North American Association of Central Cancer Registries -- has the number of cancer cases in the United States decreased.

Cancer experts agreed that the drop is good news. "The decline in both incidence and mortality together is exceptional, and has not been seen in the previous years that the report has been published," said Dr. Len Lichtenfeld, deputy chief medical officer for the national office of the American Cancer Society.

"For the most part, it is a good news story in that much of the decline can be attributed to things we have done, such as stopping smoking [for men] and getting screened for colorectal cancer."

But the study does not provide all the answers as to why the downturn may have occurred. And it remains uncertain whether the lower cancer incidence rate will be sustained in years to come.

A Mixed Bag, Doctors Say

The overall decline is mostly a function of drops in some of the most prevalent cancers. Among men, for example, lung, colorectal and prostate cancers all showed declines. Rates of breast and colorectal cancer in women also decreased.

But even among those cancers, the declines are likely less a function of one particular factor and are due more to a combination of changes in behavior and screening.

Still, noted ABC News medical editor Dr. Tim Johnson, smoking cessation likely played a yeoman's role in the downturn, particularly because it is implicated not only in lung cancer but in other cancers too.

"The most significant thing to talk about now is for people to stop smoking," he said. "There's nothing that comes close to it in terms of direct impact on cancer rates."

Dr. John Spangler, director of tobacco-intervention programs and a professor of family medicine at Wake Forest University School of Medicine in Winston-Salem, N.C., agreed. "Many of the cancers that reported declines are smoking-related, such as lung, breast and prostate cancers. So I think this is a remarkable statement on the progress of tobacco control we have made nationally."

But there is still progress to be made on the smoking front. Indeed, Gonzales' story is not one that is generally reflected in U.S. women as a group; the rates of lung cancer in women have continued to rise, even in this latest report.

Study co-author Dr. Ahmedin Jemal, an epidemiologist with the American Cancer Society, said he expects the number of women who develop lung cancer to drop in the years to come as more women, like Gonzales, choose to kick the smoking habit. But he said more support in the form of anti-tobacco legislation and state spending on smoking prevention efforts is needed to spur progress.

"The decrease in tobacco use has provided a significant opportunity to prevent cancer," he said. "Smoking accounts for nearly one-third of cancer cases, and yet many states are not properly funding tobacco control programs."

Specifically, Jemal noted, states will likely spend less than 3 percent of the $25 billion in funds they will get from the Tobacco Master Settlement Agreement of 1998 on anti-smoking efforts, a deal originally between the four largest U.S. tobacco companies and the attorneys general of 46 states. Overall, 43 million Americans continue to smoke, leaving much room for reduction in the cancers among this segment of the population.

For cancers not linked to smoking, the reasons for the downturn become slightly murkier. The decreases in colorectal cancer seen in both men and women are most likely due to improved detection, said. Dr. Michael Cummings, chairman of the Department of Health Behavior at Roswell Park Cancer Institute in Buffalo, N.Y.

"For colorectal cancer, my guess would be the declining incidence is the result of screening where polyps are found and removed ... thereby preventing cancer," Cummings said. "This essentially is an example of surgical prevention, which is very effective."

Dr. Leonard Zwelling, professor of medicine and pharmacology at the University of Texas M.D. Anderson Cancer Center in Houston, said, "Assuming this is a true drop ... people could be doing healthier things with diet and exercise; screening may be picking up early precancerous lesions and preventing them from becoming cancer by excision -- particularly colorectal."

As for prostate cancer, doctors said we could now be reaping the benefits of preventive procedures performed in the past decade.

"We 'harvested' a huge number of existing prostate cancers with PSA screening in the 1990s," said Dr. Tim Byers, deputy director of the University of Colorado Cancer Center in Aurora, Colo. "Thus, we are seeing reduced incidence now, compared to that prior period of inflated incidence."

And cancer experts speculated that a number of factors may be behind the reduction in breast cancer incidence.

"For breast cancer, most likely this relates to something that influences estrogen levels," Roswell Park's Cummings said, adding that "changes in the use of hormone replacement therapies and birth control pills" since the beginning of this decade could be part of the answer.

But when it comes to less prevalent cancers, such as liver cancer, rates are still on the rise. Study co-author Jemal said that for liver cancer, the underlying cause could be rising obesity rates. Alternatively, higher rates of infection with the hepatitis virus could be a factor.

As for kidney, thyroid and other cancers, Jemal said, "I don't really know why there is an increase."

Even the decrease seen in certain cancers may not be entirely good news, Texas' Zwelling warned.

"Scarily, fewer people could be going to the doctor due to increased uninsurance rates," he said, adding that doctors might also be less vigilant about checking for certain cancers. He noted, however, that this last scenario is unlikely.

Will the Trend Continue?

The uncertainty involved with interpreting the results could make it difficult for physicians to predict whether these trends will continue in the years to come -- or whether this year's report is a one-off bit of good news.

Still, most doctors remained optimistic.

"I think these downturns are sustainable for several reasons," Wake Forest's Spangler said. "I think people are more aware about cancer screening in general, such as mammograms for women and colonoscopy exams for everyone over the age of 50.

As more and more communities adopt smoke-free policies, there will be continued decreases in cancer rates from secondhand smoke exposure."

And Lichtenfeld of the American Cancer Society noted that even if incidence rates do not continue their decline, there is still good news to be found.

"I believe the mortality rates will continue to decline over time," he said. "That is the more sustainable trend."