For the first time since the government began compiling records, the rate of cancer has begun to decline, marking a tipping point in the fight against the second leading cause of death among Americans.
Researchers already knew that the number of cancer deaths was declining as the result of better treatment, but the drop in incidence indicates that major progress is also being made in prevention.
"The drop in incidence . . . is something we have been waiting to see for a long time," Dr. Otis W. Brawley, chief medical officer of the American Cancer Society, said in a statement. And "the continuing drop in mortality is evidence once again of real progress made against cancer, reflecting real gains in prevention, early detection and treatment."
The decline was boosted by California, largely because of a comprehensive ban on smoking. It was the only state to show declines in both incidence and deaths from lung cancer in women.
"It's a testament to the change in the lifestyle of the people of California," said Dr. Robert Figlin of the City of Hope Comprehensive Cancer Center in Duarte.
But the declines may be temporary, Figlin said. "Baby boomers are reaching the age at which they develop cancer . . . so we should not be surprised if it changes direction again."
Researchers also fear the economic meltdown may trigger an increase in incidence with fewer people willing to pay for screening tests and increased stress leading others to resume smoking. The growing number of unemployed also means fewer people have health insurance.
The report was compiled by the National Cancer Institute, the American Cancer Society, the Centers for Disease Control and Prevention and the North American Assn. of Central Cancer Registries.
The report was published online Tuesday in the Journal of the National Cancer Institute.
Incidence rates for all cancers combined and for men and women combined dropped by 0.8% per year from 1999 through 2005, with the rates for men dropping about three times the rates for women. The overall trend did not become clear, researchers said, until the data from 2005 were included.
African Americans had the highest rates of cancer, but the decline in that group was similar to that among whites. The only ethnic groups for which rates did not decline were American Indians and Alaska Natives.
The overall death rate declined by an average of 1.8% per year over the same period.
The incidence for men in 2005 was 562 cases per 100,000 people; for women it was 417 per 100,000. The death rates were 234 per 100,000 for men and 159 per 100,000 for women.
About 1.4 million Americans are diagnosed with cancer each year and an estimated 560,000 die from it. Heart disease, the nation's No. 1 killer, causes 652,000 deaths a year.
The decline in both incidence and death rates was due in large part to declines in five of the six most common cancers -- lung, colorectal and prostate in men and breast and colorectal in women. The sixth most common form, lung cancer in women, leveled off.
Those cancers alone account for about half of new cases and deaths.
"Lung cancer is the big one when it comes to cancer in the United States," said Dr. John Glaspy of UCLA's Jonsson Comprehensive Cancer Center.
According to the U.S. surgeon general, cigarette smoking accounts for 30% of all cancer deaths.
Eighty percent of those deaths are from lung cancer, but smoking also causes cancer of the oral cavity, pharynx, larynx, esophagus, stomach, bladder, pancreas, liver and kidney, among others.
Much of the decline in cancer incidence is due to widespread reductions in smoking, the report concluded.
"It's very tough for anybody not to conclude that social trends [against] smoking are having major effects on human life," Glaspy said.
California's comprehensive smoking bans and anti-tobacco education programs funded by cigarette taxes have been having a major impact, experts said. In all the other states, the incidence of lung cancer either was stable or increased.
Lung cancer death rates for men in California dropped an average of 2.8% per year from 1996 through 2005, more than twice the rates seen in states in the Midwest and South. The smoking rate is as much as three times higher in other states.
The decline in breast cancer incidence is most likely due to the sharply reduced use of hormone replacement therapy beginning in 2002, as has been noted in several previous studies.
The drop in colon and rectal cancer, the report said, most likely stems from increases in screening, which leads to the identification and removal of polyps before they become cancerous.
It is not clear why the incidence of prostate cancer has declined, but it may be a result of a leveling off in screening since 2002, the report's authors said.
Brawley of the American Cancer Society cautioned that the decline in incidence could be the result of decreased screening or other changes in screening practices.
Overall, the incidence rates dropped for 10 of the top 15 cancers.
But not all the news is good.
For men, the incidence is rising for cancers of the liver, kidney and esophagus, as well as for melanoma, non-Hodgkin lymphoma and myeloma.
For women, the incidence is rising for cancers of the thyroid, pancreas, and brain and nervous system, and for leukemia.
"This report gives us a better understanding of where we may need to redouble our efforts and try to find new ways of preventing . . . kidney, liver and other cancers that continue to show increases in both mortality and incidence," Dr. John E. Niederhuber, director of the National Cancer Institute, said in a statement.