WEDNESDAY, Dec. 31, 2014 (HealthDay News) -- Progress in the war against cancer has triggered a 22 percent drop in U.S. deaths over the past two decades, translating to about 1.5 million lives saved, a new American Cancer Society report finds.
Even so, the annual report also predict that within a few years, cancer will overtake heart disease as the leading killer of Americans.
That's because "the decrease in mortality rates from heart disease has been much larger than the decrease in mortality from cancer," said Dr. Ahmedin Jemal, the cancer society's vice president of surveillance and health services research.
"Cancer is a collection of maybe 200 diseases," he explained. "It's not like heart disease, where you have maybe some variation but it is a single entity compared to cancer."
In 2011, the most recent year for which statistics are available, heart disease claimed the lives of more than 308,000 men and 288,000 women in the United States, while cancer killed more than 302,000 men and 274,000 women.
The cancer report estimates there will be more than 1,658,000 new cancer cases and over 589,000 cancer deaths in the United States in 2015 -- about 1,600 cancer-related deaths a day.
However, those numbers are still a significant improvement on the past: The report found that cancer death rates declined from about 215 per every 100,000 people in 1991 to about 169 per 100,000 in 2011.
Convincing Americans to quit smoking has been the major driver in reducing cancer deaths, Jemal said. The number of smokers has been cut in half, and now represents fewer than one of every five people in the United States.
As a result, the lung cancer death rates dropped 36 percent between 1990 and 2011 among males, and 11 percent between 2002 and 2011 among females.
Increased use of early detection tools -- such as mammography, colonoscopy and cervical exams -- has also had a tremendous impact on the war against cancer, Jemal said.
Gains for men slightly exceeded those for women. Between 2007 and 2011, the average annual decline in cancer death rates was larger for men (1.8 percent) than women (1.4 percent), the report found.
Jemal also noted that during the past two decades, deaths from colon and prostate cancer have been nearly cut in half, and breast cancer deaths have dropped by a third.
"Really, it's due to screening, as well as improved treatment," he said. "It's really remarkable."
Progress varied by geographic region, however. The smallest declines in cancer deaths generally occurred in the South, where drops were about 15 percent. The biggest advances took place in Northeastern states, with the cancer death rate dropping 25 percent to 30 percent in Maryland, New Jersey, Massachusetts, New York and Delaware.
States that made less progress in fighting cancer likely have large populations of people who are poor or uninsured, which means they don't have access to the kind of health care that can detect or prevent cancer, Jemal believes.
In addition, these states often have policies that hamper cancer prevention -- for example, cigarette taxes may be too low to discourage smoking. "If you look at the southern states, their excise taxes on tobacco are the lowest in the nation," Jemal said.
The overall rate of cancer cases (incidence) remained stable for women between 2007 and 2011, but declined by 1.8 percent per year for men.
Men experienced relatively rapid declines in cases of colon cancer (3.6 percent per year), lung cancer (3 percent per year) and prostate cancer (2.1 percent per year) during that period, the report found.
But there's been no change in incidence rates for breast cancer. And the report found that certain cancers are even on the rise. For example, thyroid cancer cases increased an average 4.5 percent per year between 2007 and 2011, and liver cancer cases have increased by more than 3 percent.
The increase in liver cancer cases is largely due to hepatitis C infection, mainly through intravenous drug use and sharing needles in the 1960s, 1970s and 1980s, Jemal said.
The rise in thyroid cancer cases cannot be easily explained, Jemal said. Some suspect the condition may be now overdiagnosed due to the overuse of imaging scans and ultrasound, he said, but there's also been an increase in the size of cancerous lesions found.
"For thyroid, it's very difficult to explain what's occurring," he said.
To learn more about cancer, visit the American Cancer Society.