CHICAGO -- Some strains of the common sexually transmitted disease chlamydia appear to raise women's risk of cervical cancer as much as sixfold, researchers say.
Another common sexually transmitted disease, human papillomavirus, or HPV, is known to be the leading cause of cervical cancer, but the risks of chlamydia have been much less clear.
The new findings, based on 128 women with advanced cervical cancer in Finland, Sweden and Norway, appear in Wednesday's Journal of the American Medical Association.
The findings "suggest that cervical malignancy should be added to the complications and costs associated with genital chlamydial infections," Dr. Jonathan Zenilman of Johns Hopkins School of Medicine wrote in an accompanying editorial.
Chlamydia is the most common bacterial STD in the United States, with between 4 million and 8 million new cases reported yearly. Unlike HPV, it can be treated with antibiotics, but many women have no symptoms and the disease can cause pelvic inflammatory disease and infertility.
About 13,000 cases of cervical cancer are diagnosed annually, and though Pap tests can detect many cases in early, treatable stages, it kills about 4,600 women each year.
The researchers, led by Dr. Tarja Anttila of Finland's National Public Health Institute, examined data on women diagnosed with cervical cancer at least a year after having blood tests during health exams.
Blood was measured for exposure to 10 types of chlamydia. Three specific types were linked to cervical cancer, and one known as serotype G carried the highest risk. Women with that type of chlamydia were about 6.5 times more likely to develop cervical cancer than uninfected women.
The researchers took into account the effects of HPV and smoking, another risk factor for cervical cancer.
How a bacterial infection such as chlamydia might cause cancer is unclear, the researchers said, but they noted that other research has linked abnormal cell changes and the body's response to infection.
In the editorial, Zenilman called the study intriguing but not conclusive since there may have been other behavioral or biological factors that contributed to the cancer risk. Still, Zenilman said, the findings may provide another reason to expand screening for chlamydia.
National Institutes of Health: http://www.niaid.nih.gov/factsheets/stdinfo.htm
American Cancer Society: http://www.cancer.org