Between 1991 and 2012 in the U.S., the cancer death rate dropped 23 percent — more than 1.7 million cancer deaths were averted, the American Cancer Society (ACS) reports in its recent report, Cancer Statistics. But even so, the ACS finds cancer is now the leading cause of death in 21 states.

"We're gratified to see cancer death rates continuing to drop. But the fact that cancer is nonetheless becoming the top cause of death in many populations is a strong reminder that the fight is not over," Dr. Otis W. Brawley, chief medical officer of the ACS, said in a statement. Since its peak in 1991, the decline in cancer death rates over the past two decades were driven by continued decreases in mortality for four major cancers: lung, breast, prostate, and colon.

The ACS reported death rates are down for female breast cancer by 36 percent, while rates for prostate and colorectal cancers have plummeted a bit more, about 50 percent. The mortality rates for lung cancer dropped 38 percent in the past 20 years among men, and 13 percent between 2002 and 2012 among women. Researchers attributed the decline in cancer mortality rates to smoking cessation, and advances made in cancer prevention, early detection, and treatment.

Although cancer remains the second leading cause of death nationwide, it has surpassed heart disease as the top cause of mortality in 21 states, including Minnesota, Florida and Massachusetts. This is primarily due to a large reduction in deaths from heart disease.

"The decline in cardiac death rate has been faster, steeper than the decline in cancer death rate," Brawley said in response to the analysis of leading causes of death by state. For example, in Minnesota, the death rate for heart disease is 30 percent below the national average compared with a 6 percent lower death rate of cancer.

Brawley said he doesn't think the two diseases should be "competing" against each other since they share many of the same risk factors, including tobacco use, obesity and lack of physical activity. "I think we need to realize that some of the causes of heart disease are major causes of cancer," he said.

In addition, cancer is the leading cause of death among adults aged 40 to 79 years, and among Latinos and Asian/Pacific Islanders, who together make up one-quarter of the U.S. population.

"Cancer is in fact a group of more than 100 diseases, some amenable to treatment; some stubbornly resistant," Brawley said. "So while the average American's chances of dying from the disease are significantly lower now than they have been for previous generations, it continues to be all-too-often the reason for shortened lives, and too much pain and suffering."

Heart disease remains the top cause of death overall in the U.S. In 2012, 24 percent of deaths were from heart disease, compared to 23 percent of deaths from cancer.

The ACS also estimates that there will be 1,685,210 new cancer cases and 595,690 cancer deaths in the U.S. this year.

Source: Siegel RL, Miller KD, and Jemal A. Cancer statistics, 2016. CA: A Cancer Journal for Clinicians. 2016.