For the first time since the U.S. government began compiling records, the rate of cancer has declined, 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 being made in prevention.

"The drop in incidence ... is something we have been waiting to see for a long time," said Otis Brawley, chief medical officer of the American Cancer Society. 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."

But the declines may be temporary, said Robert Figlin of the City of Hope Comprehensive Cancer Center in Duarte, Calif. "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 that the economic meltdown may trigger a new increase in incidence as fewer people feel comfortable paying for screening tests and increased stress leads some people to resume smoking. The growing number of unemployed also means fewer people with 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 Association of Central Cancer Registries. The report was published online Tuesday in the Journal of the National Cancer Institute.

Incidence rates of all cancers combined and in for men and women combined dropped by 0.8 percent per year from 1999 through 2005, with the rates for men dropping at about three times the rate for women. The overall trend did not become clear, researchers said, until the data from 2005 were included.

Blacks 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 Alaskan natives.

The overall cancer death rate declined by an average of 1.8 percent per year over the same period.

The incidence for men in 2005 was 562 cases per 100,000 individuals, while that for women was 417 per 100,000. The death rates were 234 per 100,000 men and 159 per 100,000 women.

About 1.4 million Americans are diagnosed with cancer each year, and an estimated 560,000 die of it.