Lung cancer is surpassing breast cancer as the most common cause of cancer death among women in the world's wealthy nations, a report says.

Lung cancer has been the biggest cancer killer of men for decades, but smoking by women has increased dramatically in the last four decades and the results are just now being seen in developed countries, the report by the American Cancer Society says.

Lung cancer is nearly always the result of smoking, says epidemiologist Lindsey Torre, lead researcher for the society's report.

"But it takes about two to three decades to see lung cancer deaths due to smoking, because lung cancer does take a long time to develop," she says.

"The lung cancer deaths we are seeing today really have to do with smoking trends we saw in the 1970s, when women really started to pick up smoking," says.

The increase has come while death rates from breast cancer have remained stable or even decreased in developed countries as a result of early detection combined with improved treatments, she notes.

In comparison, the rates of lung cancer and associated deaths in such countries are expected to go up as more people take to smoking, says Dr. Norman Edelman, a consultant for scientific affairs at the American Lung Association.

"As people emerge from poverty, people start adopting bad Western habits like smoking, so cancer rates are going up, especially lung cancer rates in men," he says.

As the world's developing countries increasingly move toward a Western lifestyle, some cancers once rarely seen have become more common, and cases of breast, lung and colon cancer are also on the rise, the researchers say.

The American Cancer Society's report shows there were about 14 million new cancer cases and 8 million cancer deaths in 2012, the most recent year for which data from the International Agency for Research on Cancer is available.

In the United States, lung cancer has been the main cancer killer for men since the 1950s, and for women it has been so since the late 1980s, reflecting rising trends in U.S. smoking rates.

However, recently the smoking rates in many developed countries have leveled off or dropped, and in the United States "we are already seeing lung cancer death rates decline," Torre says.

Half of all cancers are preventable, and the best way to prevent lung cancer is to stop smoking, or better yet, don't start, she says.

Even quitting in middle age can avoid 60 percent of the risk of death from lung cancer, she emphasizes.

"It's never too late to quit."

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