Researchers led by Pentii Koskela, PhD, of the National Public Health Institute in Oulu, Finland, studied 182 women who had cervical cancer, analyzing their blood samples for antibodies to C. trachomatis and then comparing the samples to those of cancer-free patients. The results of the study were published in a recent issue of the International Journal of Cancer (Vol. 85, Issue 1).

"Women who had serum antibodies to C. trachomatis were 2.2 times more likely to develop cervical squamous cell carcinoma," Dr. Koskela said. Squamous cell carcinoma is the most common type of cervical cancer, accounting for 85 percent to 90 percent of cases. Some of the patients smoked and were infected with the human papillomavirus (HPV), both of which are associated with cervical cancer. Both smoking status and HPV infection were factored into the research, so that risk from C. trachomatis was calculated independently, according to the researchers. Because both HPV and Chlamydia are sexually transmitted, women with one infection are at greater risk of having the other.

Dr. Koskela estimated C. trachomatis could be responsible for as many as 10 percent to 15 percent of current cervical cancer cases, although HPV is still considered the leading cause of cervical cancer.

How could infection with this bacteria cause cervical cancer? "The relationship between bacterial infections and cancer is not clear," Dr. Koskela said. "As far as we know, C. trachomatis is the only bacterium that has been linked to cervical cancer."

He believes the bacteria could trigger inflammation, leading to DNA mutations, and eventually cancer. Dr. Koskela also believes bacterial infections could prevent the death of damaged cells that would normally die rather than progress to cancer.

Other experts have questioned these results. "This study uses vast pooled data among three nations to try to answer important questions, but I worry that the conclusions may be premature. There are many unanswered questions," said Annekathryn Goodman, MD, a gynecologist and obstetrician at Massachusetts General Hospital in Boston.

Also, women may not know if they had been exposed to the C. trachomatis bacteria, Dr. Goodman said. She added that "although practitioners can perform a separate test for Chlamydial infections, usually at the same time as the Pap smear, Chlamydial infections can be completely without symptoms." Chlamydial infections can cause infertility and may play a role in premature labor. "The good news is that these infections are easy to treat with antibiotics," Dr. Goodman said.

Elizabeth Unger, MD, PhD, acting chief of the human papillomavirus section at the Centers for Disease Control and Prevention, said the study’s findings are interesting but she considers them tentative.

Serology, the HPV test used in this study, has limited sensitivity, meaning the test gives false negative results in some women with current or past HPV infection. Consequently, all or part of the increased risk attributed to Chlamydia may be due to its association with undetected HPV infection. Also, "the effect they see is very modest, and interestingly, does not extend to all types of cervical cancer," Dr. Unger said.

As far as the next step in this line of research, Dr. Koskela said he will look at different types of C. trachomatis to see if there are any differences in their ability to cause cervical cancer. "We hope that our results will generate increased interest in the relationship between bacterial infection and cancer," he said.

Precancerous and cancerous changes of the cervix can usually be detected by the Pap test. This test involves scraping some cells from the surface of the cervix and looking at them under a microscope. Because precancers and very early cervical cancers are almost 100 percent curable, this test can prevent almost all deaths from cervical cancer.

The American Cancer Society (ACS) estimates 12,800 cases of invasive cervical cancer will be diagnosed in the US this year, and about 4,600 women will die from the disease.