Secondhand smoke (search) may raise the risk of developing cervical cancer (search), say Johns Hopkins University researchers. They report their findings in the January issue of Obstetrics and Gynecology.

The evidence was more than 40 years in the making. It traces back to census data taken in the 1960s and 1970s.

First, the researchers examined census smoking data from 1963 and 1975 in Washington County, Md. They focused on women aged 25 or older who hadn’t had cancer before and who disclosed information on smoking in their households. That included more than 24,000 women from each census.

Next, the researchers matched information to the county’s cancer registry.

In the 1975 data, women exposed to cigarette smoke at home had a higher risk of developing cervical cancer. “Women who lived with smokers had a 40 percent or greater risk of developing cervical [cancer],” says researcher Anthony Alberg, PhD, MPH, in a news release.

The association was stronger with the 1963 census. Women from that census who lived with a smoker had twice the cervical cancer risk of those who did not.

The risks for women who were smokers themselves were a bit different. Women smokers were more than two and a half times more likely to develop cervical cancer in the 1963 census. Yet in the 1975 census, women smokers had more than one and a half times the risk of cervical cancer.

There were other differences between 1963 and 1975. The percentage of women who had never smoked but lived with a smoker dropped from 25 percent to 15 percent. In addition, more women (15 percent) were former smokers in 1975, compared with 9 percent in 1963.

Scientists had already linked smoking cigarettes to increased cervical cancer risk. But they stop short of calling it a definite cause of cervical cancer, since other factors (like sexual history) could be at work.

Not surprisingly, smokers had a higher cervical cancer risk than nonsmokers living with a smoker. In the 1963 group, 37 percent of cervical cancer cases were found in smokers who lived with another smoker, while 13 percent occurred in nonsmokers who breathed secondhand smoke at home.

Those numbers were lower in the group of 1975 census participants. Among those women, 17 percent of cervical cancer cases stemmed from active smoking as well as passive smoking, while 4 percent could only be traced to secondhand smoke.

The reason for the difference isn’t fully understood. However, “our results point toward a role for passive cigarette smoking as a risk factor for cervical [cancer],” say the researchers.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Trimble, C. Obstetrics and Gynecology, January 2005; vol 105: pp 174-181. News release, Johns Hopkins University.