In a new analysis of global cancer statistics, less-developed countries account for about 57 percent of cancer cases and 65 percent of cancer deaths.
Aging populations are one factor, researchers say, as is economic development and urbanization, which can bring with them a rise in cancers related to obesity, smoking, lack of exercise and sexually transmitted diseases.
Worldwide, there were about 14.1 million new cancer cases in 2012 and about 8.2 million cancer-related deaths.
"The cancer burden is quite substantial worldwide," said Lindsey Torre, an epidemiologist at the American Cancer Society in Atlanta, who led the study. "It's not just in developed countries, but in developing countries, which is something that people don't realize."
In the developed world, lifestyle choices made long ago are still haunting women, for whom lung cancer has displaced breast cancer as the number one cause of cancer deaths, the researchers found.