Smoking cigarettes while infected with a virus linked to cervical cancer increases the risk for the disease, researchers have found.

The risk of cervical cancer — of the type confined to the surface layer of the cervix — was higher among smokers with high levels of human papillomavirus Type 16, which is most closely linked to the cancer.

"Our initial analyses centred on whether smoking was an independent risk factor for cervical cancer," said the study's lead author, Dr. Anthony Gunnell, of the Karolinska Institute in Stockholm.

In the study, Gunnell's team compared levels of HPV-16 in cervical smears and smoking among 275 women with the disease and 363 controls.

Current smokers with HPV-16 had a 14-fold increased risk over women who tested negative for the virus and smoked, the researchers report in the November issue of Cancer Epidemiology, Biomarkers & Prevention.

In women who were smokers and had high virus levels, the risk jumped 27-fold compared with non-smokers who were negative for HPV-16.

Non-smoking women with high virus loads had a six-fold risk compared with HPV-negative non-smokers, the researchers said.

The findings suggest a synergistic relationship between HPV and smoking that greatly increases the likelihood of developing cervical cancer, Gunnell said. "This would put them in a risk group worthy of careful monitoring."

There was also a link between smoking duration and cancer. Localized immune suppression, the fuelling of tumour growth or a combination could be behind it, Gunnell speculated.

The research was supported by the U.S. National Institutes of Health, the Swedish Cancer Society and the Danish National Research Foundation.