HPV, the human papillomavirus, is vastly more dangerous in women who smoke, a Swedish study finds.
Some 19 kinds of HPV have been linked to cervical cancer; HPV-16 is the most deadly.
Now, research suggests that women who smoke are more likely to get cervical cancer if they become infected with that virus than are nonsmokers.
While the nonsmokers studied were six times as likely to develop cancer if infected, smokers were more than 14 times as likely to get cancer within nine years if they had the virus, according to the study.
Researchers Anthony S. Gunnell and his colleagues at Sweden's Karolinska Institute suspected smoking and HPV-16 might work together.
So they compared the medical records of 375 women who had the earliest stage of cervical cancer to the records of 363 women with similar characteristics who did not have the cancer.
Based on Pap smears taken an average of nine years before the women developed cervical cancer, the researchers were able to tell whether the women had had an HPV-16 infection.
They also were able to see whether the women had had high or low levels of HPV in their blood -- something doctors call high or low viral load.
--Among smokers, those who had tested positive for HPV-16 were 14.4 times more likely to get cervical cancer than those who did not have the infection.
--Among smokers, those who had had high HPV-16 viral load were 27 times more likely to get cervical cancer than those who did not have the infection.
--However, among nonsmokers, those who had tested positive for HPV-16 were only six times more likely to get cervical cancer than nonsmokers who did not have the infection. Having high vs. low HPV-16 viral load did not affect that statistic.
Women who had continued to smoke further multiplied their chances of getting cervical cancer.
The researchers suggest smoking may help HPV-16 grow faster -- possibly by slowing helpful immune responses.
They also suggest smoking may speed the process by which HPV-16 causes cancer.
The findings appear in the November issue of Cancer Epidemiology, Biomarkers & Prevention.
By Daniel J. DeNoon, reviewed By Louise Chang, MD
SOURCES: Gunnell, A. Cancer Epidemiology, Biomarkers & Prevention, November 2006; vol 15: pp 2141-2147. News release, American Association for Cancer Research.