New hypothesis proposed for how chlamydia might increase cancer and ectopic pregnancy risk

Scientists at the University of Bristol and the University of Edinburgh have proposed a possible means through which chlamydia infections could lead to an increased risk of cancer and ectopic pregnancies.

Following a review of evidence from lab-based studies, animal models and clinical studies, scientists found that chlamydia – the most common bacterial sexually transmitted infection worldwide – stimulates a change in reproductive tract cells. This change, known as ‘epithelial-to-mesenchymal transition’ (EMT), can lead to inflammation and cell growth.

Researchers proposed that this cellular change contributes to the development of further reproductive tract disease including cancer and ectopic pregnancies. Their study found that chlamydia may also be linked to the way that pelvic inflammatory disease is triggered in some women.

Lead investigator Dr Paddy Horner, from the National Institute for Health Research (NIHR) at the University of Bristol said: “Chlamydia is a bacterial infection that stimulates EMT, which may persist after the chlamydia infection has cleared.

“We think that the association of chlamydia with ovarian and cervical cancer could be explained by the persistence of EMT changes in combination with DNA damage caused by chlamydia following chlamydia infection.

“Also, we know that EMT cells impair the integrity of the lining of the infected reproductive tract cell, making it more susceptible to invasion by other bacteria. This increases the risk of pelvic inflammatory disease from those invading bacteria.

“Furthermore, epithelial (barrier) cells in the fallopian tube that have previously been infected with chlamydia have more receptors on their surface, which are associated with an increased risk of ectopic pregnancy. There is evidence that these cell surface receptor changes could be caused by EMT.

He added: “If our hypothesis about the role of EMT following chlamydia infection in women is correct, it could help explain some of the recent epidemiological observations about chlamydia and reproductive disease which are difficult to account for using current concepts about the immune response to chlamydia.

“It would also support the English National Chlamydia Screening Programme’s shift to earlier testing of women, as the shorter the duration of infection, the lower the risk of developing EMT changes.

“Further down the line, this could lead to the development of new tests for identifying women at increased risk of ovarian cancer and ectopic pregnancy and interventions could reduce these risks.”

While Dr Horner acknowledged that significant research remained to be done in order to validate their hypothesis that cellular changes following chlamydia infection leads to greater risks of cervical and ovarian cancer, and ectopic pregnancy, he said that this research could hold crucial benefits for patient care and disease prevention.

Reacting to the findings, Munira Oza, the director of the Ectopic Pregnancy Trust, said: “This analysis helps to further our understanding of one of the possible risk factors for ectopic pregnancy and we would welcome more research in this area.

“It also highlights the importance of the change of focus of the National Chlamydia Screening Programme to opportunistically making proactive offers of a chlamydia test to young people without symptoms to reduce the risk of reproductive harm.

She added: “With early detection through the screening programme and much-needed education to reduce the stigma of chlamydia, we hope that many women and families might be spared the health risks and heartache of ectopic pregnancy. We encourage young women to screen when given the opportunity”.

It is currently recommended that sexually active women under the age of 25 be tested for chlamydia annually.

The study was published in the Journal of Infectious Diseases.