Chlamydia increases risk of cervical cancerBMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7278.71 (Published 13 January 2001) Cite this as: BMJ 2001;322:71
Infection with certain subtypes of chlamydia, a bacterium which is commonly transmitted sexually, greatly increases the risk of cervical cancer, according to a new report (JAMA 2001;285:47-51).
Although infections with oncogenic strains of human papillomavirus remain the prime cause of cervical cancer, infection with some strains of Chlamydia trachomatis seem to contribute to that risk.
The finding is important because chlamydia, though frequently asymptomatic, is one of the most common sexually transmitted diseases and can be treated with appropriate antibiotics. In the United States, between four million and eight million new cases of chlamydia are reported yearly.
The bacterium—which, when symptomatic, causes purulent discharge, dysuria, and urethritis—can also cause ascending infections leading to pelvic inflammatory disease and infertility. Previous studies indicated that chlamydia is a risk factor for cervical cancer (International Journal of Cancer 2000;85:35-9). Though an association had been established, it was unknown if the risk was type specific.
Led by Dr Tarja Anttila of Finland's National Public Health Institute, researchers from Finland, Norway, and Sweden set out to uncover the relation between infection with subtypes of chlamydia and the subsequent development of squamous cell carcinoma of the cervix.
To do so they searched national cancer registries for cervical cancer cases and linked serum banks to patients in the registries, using a longitudinal case control design. These data files were searched for cervical carcinoma cases and seropositivity for chlamydia IgG antibodies, as measured by immunofluorescence.
Exposure to oncogenic human papillomavirus types 16, 18, and 33—as well as to the tobacco byproduct cotinine—was also tested for, as these are known risk factors for cervical cancer. Infection with human papillomavirus and chlamydia was also confirmed via isolating DNA from these organisms in tissue sections of the cancer cases.
One hundred and eight one cases of invasive cervical carcinoma were identified. Most of the cases were from Norway (129), with 8 Finnish and 4 Swedish cases. In all, 150 (82%) of the cancers were squamous cell carcinomas, and the rest were adenocarcinomas. The mean age at diagnosis was 44 years.
For each of these cases, a prediagnostic serum sample was analysed and screened for exposure to 10 types (or serovars) of chlamydia. The overall prevalence rates of serum antibodies to C trachomatis was 27% among cancer cases and 13% in controls. The average time between serum donation and diagnosis of cervical cancer was 56 months.
Serum samples were obtained from three control subjects for each case—matched for age, country, and county, as well as for storage time of the samples. The 533 control subjects were free of cancer at the time of blood donation.
The researchers found that three types of chlamydia (serotypes G, I, and D) significantly increased the risk of cervical cancer. Women infected with serotype G carried the highest risk, with a 6.6-fold increased incidence over uninfected cohorts, and those infected with serotypes I and D faced a risk 4 and 2.7 times greater respectively.
Moreover, the researchers found that exposure to multiple strains, or to more than one serotype, also increased the risk of squamous cell cervical cancer. Adenocarcinoma of the cervix did not seem to be associated with chlamydia.
Although the study is interesting, it is unclear if chlamydia is an independent risk factor for cervical cancer or merely associated with it because it travels with other risk factors, such as human papillomavirus and unprotected promiscuous sexual activity.