By Alexandra Goho
A Dangerous Duo
Smoking combined with viral infection boosts cervical cancer risk
By Alexandra Goho
Here’s one more reason not to smoke: A recent study shows that smoking dramatically increases the odds of cervical cancer developing in women infected with the human papillomavirus (HPV). The findings could help public health efforts to educate women about cervical cancer risk factors and prevention.
Unlike with lung cancer and heart disease, “Women are not really aware that smoking is a risk factor for cervical cancer,” says Charlie Stayton, the executive director of the Arkansas Cancer Research Center’s Witness Project, a national education and outreach program based in Little Rock.
The vast majority of cervical cancer cases are caused by HPV—a common sexually transmitted viral infection. In most women, the infection goes away without causing any harm. However, a small fraction of infections lead to cervical cancer. Of the more than a dozen HPV types, one called HPV-16 is present in half of all cases of the disease.
Reporting in the November 2006 Cancer Epidemiology, Biomarkers & Prevention, scientists in Sweden examined the effect of smoking in combination with HPV. Epidemiologist Anthony Gunnell of the Karolinska Institute in Stockholm and his colleagues combed through the Pap smear records of more than 146,000 Swedish women. The researchers selected 738 women, half of whom had been diagnosed with early stage, noninvasive cervical cancer. The other half had never been diagnosed with cervical cancer.
The researchers found that among nonsmoking women, those infected with HPV-16 had about five times the risk of developing cervical cancer compared with women who tested negative for the virus. (They controlled for other known cervical cancer risk factors including sexual activity and oral contraceptive use.) That result was no surprise.
Yet, when the researchers looked at women who smoked, the difference between the two groups was dramatic. Smokers infected with HPV-16 were 14 times more likely to develop cervical cancer than those without the virus. A woman’s risk varied depending on the amount of virus in her body. Smokers with high levels of the virus were 27 times more likely to develop cervical cancer compared with smokers who didn’t have HPV-16. Even more striking, long-time smokers (five years or more) who tested positive for the virus had 36 times the risk compared with long-time smokers without HPV-16.
Although it’s unclear how smoke interacts with HPV in the body, scientists have proposed several theories. Gunnell suspects that smoking suppresses the immune system, rendering it less effective at clearing HPV from the body or controlling abnormal cell growth in the cervix. “Either or both of these effects would increase the risk of cervical cancer,” he says.
Laura Koutsky, an epidemiologist and HPV expert at the University of Washington in Seattle, says the data are consistent with previous studies showing that among women infected with the virus, those who smoke are about two to three times more likely to develop cervical cancer compared with nonsmokers.
Koutsky says awareness is growing about the role of HPV in cervical cancer since the U.S. Food and Drug Administration approved a vaccine against certain types of HPV in June 2006. “It has great potential for young girls and adolescents,” she says. But for some women in their 20s and over, the vaccine will not provide as much protection. That’s because a higher percentage of those women are already infected with HPV, she says. “But what they can do is stop smoking.”