(USA TODAY) -- Cancer now kills more people worldwide than AIDS, tuberculosis and malaria combined, and more than half of deaths are in developing countries.

Yet many people, including policymakers, still harbor the misconception that cancer is a concern only for industrialized nations, rather than developing countries.

Cancer activists will try to dispel such myths today as they mark World Cancer Day, organized by the Union for International Cancer Control, a global health group.

Some cancers are more common in poor countries partly because access to health care and preventive services is lacking. For example, 85% of cervical cancer deaths are in developing countries, according to the cancer union.

Cancer rates are increasing in developing nations for many reasons. As poor countries industrialize, people are exposed to more hazardous chemicals, says Otis Brawley, chief medical officer at the American Cancer Society.

Cigarette companies also market their products heavily overseas. As more people take up smoking, lung cancer rates are rising, says Cy Stein, deputy director of clinical research at City of Hope Medical Center's cancer center in Duarte, Calif. Nearly 80% of the world's 1 billion smokers live in low- or middle-income countries, according to the World Health Organization.

"It's a perfect storm: more urbanization, with more fast food and more inactivity," says Katie Horton, a research professor with the George Washington University School of Public Health and Health Services in Washington, D.C.

Yet developing nations often are ill-equipped to care for cancer patients, Brawley says. Many dying patients lack even the basics, such as adequate pain relief, he adds. According to the Union for International Cancer Control, 99% of patients with "untreated and painful deaths" live in developing nations.

"Pain relief is cheap to do, and should logistically be easy to do, but it's not being done," Brawley says. "It's an issue of human suffering."

And 90% of the global consumption of opioid analgesics, such as morphine, is in just five regions: Australia, Canada, New Zealand, the USA and Western Europe. Less than 10% of these pain relievers are used by the other 80% of the population, the cancer union says.

Cancer survivors and advocates will try to spread their message in a variety of ways. Brawley will lead a Twitter chat today at 11 a.m. ET, using the hashtag #WorldCancerDay.

He also will lead a Google Plus chat and live video broadcast at 3 p.m. ET. The American Cancer Society also will light the Empire State Building in orange and blue to draw attention to the cancer fight.

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