CALIFORNIA: Lung cancer rates have been falling across the United States over the past decade, but deaths from the disease are steady or rising among middle-aged women in the South and Midwest, according to a study based on more than one million women.

The findings, published Monday in the Journal of Clinical Oncology, point to a need for more aggressive political action and strategies for reducing smoking by a new generation of men and women in all US states, researchers said.

"Yes, we are making progress in reducing death rates for lung cancer, but there is really a new epidemic and we have to pay attention to increasing death rates in women," said Ahmedin Jemal, the study's lead author and a researcher at the American Cancer Society in Atlanta, Georgia.

Lung cancer currently accounts for about one in four cancer deaths in the US, making it the top cancer killer, according to the Centers for Disease Control and Prevention.

But lung cancer deaths among both men and women have been steadily declining since the 1990s, a trend usually credited to public health campaigns and state policies, like cigarette taxes and smoking bans, designed to encourage people to quit smoking and discourage young people from starting.

Previous research has shown that women born in 1950 and afterwards are an exception to the recent decline.

Social trends during the 1960s and 1970s, when these women would have taken up smoking in their teens and early adult years, are usually blamed.

But Jemal's team, with colleagues at the National Cancer Institute, looked at national mortality data to see whether there were any regional patterns as well.

The study is based on data for more than one million US white women aged 35 to 84, who died of lung cancer between 1973 and 2007. The researchers compared 23 states, including 10 in the south and six in the Midwest, and California and New York.

Between the 1970s and 2007, the risk of dying from lung cancer was highest among women born in the 1930s. Rates then dropped off among women born during the following decade.

When it came to baby boomers, post-World War II babies of the late 1940s and 1950s, the numbers of young women dying of lung cancer rose again but only in some states.

In Alabama, for example, deaths per 100,000 increased from 6.9 to 10.7 among women aged 40 to 44. In contrast, deaths fell from 6.1 to 2.8 per 100,000 in the same age group in California.

Similar patterns emerged in other southern states and in the Midwest, while California and New York showed steady declines. Jemal said that weak anti-smoking political action could be the reason more women are dying in the southern and midwestern states, noting that California was a leader in aggressive tobacco control policies - though he added that tying the decreasing lung cancer death rate to that was still only speculation at this point.

Some experts said the study was limited by a lack of information on smoking rates and differences in lung cancer care and treatment.

"I think we all know that smoking is the dominant cause of lung cancer, and that rates of smoking have come down. But a sizable section of the US population still smokes and we have to find a way to get the message out that smoking is hazardous," Jemal said.