About half of bladder cancer cases in women age 50 and older are now traceable to smoking, up from 20 or 30 percent in earlier decades, researchers report. The finding means women have now caught up to men in the percentage of bladder cancers attributable to cigarettes.
In addition, current smokers are four times as likely to develop bladder cancer as people who have never smoked, up from the threefold increased risk seen in earlier studies. Together, the findings reflect the fact that the decline in smoking among women has lagged behind the drop seen in men, and suggest that changes in cigarette composition in the past 50 years are altering cancer risk, the researchers propose in the Aug. 17 Journal of the American Medical Association.
“This is an important, and sad, finding,” says Anthony Alberg, a cancer epidemiologist at the Medical University of South Carolina in Charleston, who wasn’t involved in the new study.
“This was not a random sample, but the fact that it represents several states adds to the generalizability of the overall study.”
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In 2009, roughly one in five U.S. adults — more than 23 percent of men and about 18 percent of women — smoked, according to the Centers for Disease Control and Prevention. While the figures represent a steady decline, the percentage of men who smoke has fallen more than that of women since the 1960s, when roughly 52 percent of men and 34 percent of women smoked. The gender disparity in smoking rates tracks with disparities in bladder cancer rates decades later.
The people in the new study were age 50 to 71 when researchers initially contacted them in the mid-1990s. Many no doubt started smoking in their teens, says study coauthor Neal Freedman, a molecular biologist and epidemiologist at National Cancer Institute in Bethesda, Md. Since cancer can take years or decades to develop, the long-term gender trends probably explain why the percentage of bladder cancers in each group attributable to smoking has evened out at about 50 percent, he says.
Freedman and his colleagues analyzed data from more than 280,000 men and 186,000 women from eight states who answered questions about their health, smoking history, alcohol intake, diet, physical activity and other lifestyle factors. Researchers tracked the group through 2006, noting how many people developed bladder cancer.
“It seems that the relative risk is becoming stronger,” says Freedman, who notes that cigarettes aren’t what they were a half century ago, when they were first linked to bladder cancer. “There have been changes in types of tobacco, the way it is cured, even the construction of cigarettes — with filters.”
Studies have noted that some chemicals have been added to cigarettes over the years, including a bladder carcinogen called beta-napthylamine. But little is known about other chemicals some cigarettes might contain and, in this study, what brands people smoked, Freedman says.
Alberg says the change in cigarette composition “is the most likely explanation” for the increased bladder cancer risk. But until regulators can get a clearer picture of cigarette additives, specifics will be difficult to pin down, he says.