"It's dropping fast enough that another disease is eclipsing it," said Dr. Walter Tsou, president of the American Public Health Association.
The single biggest reason: fewer smokers.
The news is contained in the American Cancer Society's annual statistical report, released Wednesday. In 2002, the most recent year for which information is available, 476,009 Americans under 85 died of cancer compared with 450,637 who died of heart disease.
That trend actually began in 1999, but "this is the first time we've looked at this by age," said Ahmedin Jemal, a cancer society epidemiologist and main author of the report.
Those under 85 comprise 98.4 percent of the population, said Dr. Eric Feuer, chief of statistical research for the National Cancer Institute who also worked on the report.
That means that only the very oldest Americans continue to die of heart disease more than of cancer, a trend that is expected to reverse by 2018, said Dr. Harmon Eyre, the cancer society's longtime chief medical officer.
"This is a situation in which neither one of us wants to be No. 1" because far more deaths could be prevented, said Dr. Rose Marie Robertson, chief scientific officer of the American Heart Association.
A third of all cancers are related to smoking, and another third are related to obesity, poor diets and lack of exercise — all factors that also contribute to heart disease.
"We want to send the message: Don't smoke, eat right, exercise and maintain normal weight, and see your doctor for normal checkups," Eyre said.
Smoking among adults fell dramatically between 1965 and 2000, from 42 percent to 22 percent. Federal goals are to cut the rate to 12 percent by 2010.
Heart disease sufferers also have benefited from better surgical techniques and devices and from better drugs to treat heart problems and control factors like high blood pressure, Eyre said.
Cancer death rates have declined about 1 percent per year since 1999, thanks to earlier detection, prevention efforts and better treatments, experts said.
Deaths from colon cancer and from lung cancer in men are particularly striking.
"They're dropping so fast that they exceed the impact of aging," which increases the likelihood of developing cancer, Eyre said.
The drop in colon cancer is because of screening, which finds and removes growths called polyps before they turn cancerous. Still, about half of people for whom testing is recommended don't get checked.
In women, cancer incidence has leveled off for the first time after several years of rising.
"The lung cancer epidemic has peaked in women and we're likely to see stabilization of rates or a decline from this point on," said Dr. Elizabeth Ward, director of surveillance research for the cancer society.
The report also highlights cancers caused by germs — 1.5 million cases or 26 percent of cancers in developing countries; and 360,000 cases or 7.3 percent of cancers in developed countries like the United States.
These are mostly liver cancer, caused by the hepatitis B and C viruses; cervical cancer, caused by human papillomavirus; stomach cancer caused by H. pylori bacteria; and AIDS-related cancers caused by infection with HIV.
"Many of them are highly preventable," especially through vaccines for hepatitis and a soon-anticipated vaccine for papillomavirus, Ward said.
Tsou, of the public health association, said the task for the future is clear: "We know a lot about how to treat cancer but we need to know more about how to prevent the disease in the first place."
The cancer society's Eyre agreed.
"In cardiovascular disease, there has been a better recognition of preventable precursors," such as smoking, high cholesterol, diabetes and high blood pressure, he said.
By Marilynn Marchione