More than 1.5 million Americans avoided death from cancer since 1991 thanks to falling smoking rates and better cancer prevention, detection and treatments, according to a study from the American Cancer Society.

The overall rate of deaths from cancer decreased from about 215 per 100,000 people in 1991 to about 169 per 100,000 people in 2011, researchers found.

“Further reductions in cancer death rates can be accelerated by applying existing cancer control knowledge across all segments of the population, with an emphasis on those in the lowest socioeconomic bracket and other disadvantaged populations,” write Rebecca Siegel and her colleagues in CA: A Cancer Journal for Clinicians.

For the new report, the researchers compiled data from the National Cancer Institute, the Centers for Disease Control and Prevention and the National Center for Health Statistics.

During the most recent years with data available, 2007 through 2011, cancer cases decreased by 1.8 percent among men and remained steady among women, they found.

For those years, deaths from cancer also decreased by 1.8 percent among men and fell by 1.4 percent among women.

Although the overall cancer death rate dropped over the past two decades, the researchers also found that not all Americans benefited equally. The decline in deaths varied from state to state.

For example, declines in cancer deaths reached about 15 percent in southern states, compared to drops of 20 percent or more in northern states. Southern states also had the highest current cancer death rates.

“The large geographic variation in cancer death rates and trends reflects differences in risk factor patterns, such as smoking and obesity, as well as disparities in the national distribution of poverty and access to health care, which have increased over time,” the researchers write.

Using the same data, the authors also estimate the number of cancer cases and deaths for 2015.

Overall, they estimate that about 1.7 million cancer cases and about 590,000 cancer deaths will occur in the U.S. during the coming year.

They predict prostate cancer will remain the most diagnosed cancer among men and breast cancer the most diagnosed among women. Lung cancer will be the second most diagnosed cancer among both sexes, but will be the leading cause of cancer deaths for both sexes.

Among children ages one to 14 years, leukemia will be the most diagnosed. For older children between ages 15 to 19 years, cancers of the brain and nervous system will be most common, the researchers say.

In a statement emailed to Reuters Health, Dr. Steven Rosen, provost and chief scientific officer at City of Hope, said people should be vigilant for increasing cancer rates from a number of factors, including obesity.

“Recreational marijuana use can increase lung cancer and the rise of sexually transmitted diseases is associated with cancer risk,” said Rosen, who wasn’t involved in the new study. “In addition, cancer is associated with aging, and as life expectancy fortunately increases, cancer rates will rise proportionately.”