The incidence of new
cancer cases has been falling in recent years in the United States, the first time such an extended decline has been documented, researchers reported Tuesday.
Cancer diagnosis rates decreased by an average of 0.8 percent each year from 1999 to 2005, the last year for which data are available, according to an annual report by the National Cancer Institute, the American Cancer Society and other scientific organizations.
Death rates from cancer continued to decline as well, a trend that began some 15 years ago, the report also noted. It was published online in The Journal of the National Cancer Institute.
“Each year that you see these steady declines it gives you more confidence that we’re moving in the right direction,” said Dr. John E. Niederhuber, director of the National Cancer Institute, who is not an author of the report. “This is not just a blip on the screen.”
Death rates from cancer fell an average of 1.8 percent each year from 2002 to 2005, according to the new report. Although last year’s report said death rates dropped an average of 2.1 percent each year from 2002 to 2004, a modest 1 percent decline in 2005 lowered the average percentage for the period.
The decline is primarily due to a reduction in death rates from certain common cancers, including prostate cancer and lung cancer in men, breast cancer in women and colorectal cancer in both sexes.
The report attributes the reductions to adoption of healthier lifestyles and improved screening, as well as advances in treatment.
The drop in annual incidence rates is harder to interpret. The data may point to a real decline in the occurrence of some types of cancer, experts said. Alternatively, the decline may reflect inconsistent screening practices, causing some cancers that used to be detected to now go undiagnosed.
Breast cancer incidence rates decreased by 2.2 percent annually from 1999 to 2005, for example, a drop some researchers attributed to large numbers of women quitting hormone replacement therapy after a national study linked it to breast cancer in 2002.
Yet mammography rates have also fluctuated in recent years, meaning that some breast cancer cases may be going undetected, said Ahmedin Jemal, the strategic director for cancer surveillance at the American Cancer Society.
The incidence of prostate cancer declined by 4.4 percent a year from 2001 to 2005, after annual increases of 2.1 percent a year for several years, Dr. Jemal said. Yet prostate screening rates, too, have leveled off in recent years.
“This might not be good news,” Dr. Jemal said. “It’s always difficult to interpret the incidence rate.”
Christine Eheman, chief of the cancer surveillance branch at the federal Centers for Disease Control and Prevention, was more optimistic about the decline in cancer diagnoses.
“I do think it’s a good sign,” Dr. Eheman said, “but I think we need to be very careful not to think we have this problem in any way beaten. We need to continue to do what we know works, and also find out why some cancers are not decreasing and not decreasing in certain populations.”
Some types of cancer are being found more often, the report said. Among men, incidence rates increased for cancers of the liver, kidney and esophagus, and for melanoma and myeloma. Among women, incidence rates increased for cancers of the lung, thyroid, pancreas, brain and nervous system, bladder and kidney, and for melanoma. Rates of leukemia and non-Hodgkin’s lymphoma increased in both sexes.
The incidence of lung cancer has been declining among men for many years but rising among women, though the increase is slowing, according to the report.
“Women, unfortunately, got hooked on the smoking habit in the ’60s and ’70s,” Dr. Eheman said, “so there was a larger increase in smoking later on in time, and the prevention of smoking has been slower. The decrease in lung cancer that we hope will occur has not been happening yet.”
The report found sharp regional differences in lung cancer rates that appeared to be associated with local legislation, like smoking bans, and social attitudes toward tobacco and smoking. Lung cancer is diagnosed least often in Utah and most often in Kentucky, the report said.
State tobacco control policies appear to have had an enormous impact, the researchers said. In California, the first state to establish a comprehensive statewide tobacco control program, lung cancer death rates among men dropped by 2.8 percent annually on average from 1996 to 2005, twice the decline observed in many Southern and Midwestern states. California was the only state where the incidence of lung cancer among women had decreased.
Lung cancer death rates among women increased in 13 states: Alabama, Arkansas, the Carolinas, Indiana, Iowa, Kansas, Kentucky, Louisiana, Michigan, Mississippi, South Dakota and Tennessee. Tobacco taxes are lower than average in many of these states, the report noted.
