# Risk of cancer among individuals with a history of bacterial sexually transmitted infections: A population‐based study in Alberta, Canada

## TL;DR

This study found that people with a history of bacterial STIs like chlamydia, gonorrhea, or syphilis have an increased risk of certain cancers compared to the general population.

## Contribution

The study is one of the first to quantify cancer risk following bacterial STIs using population-based data and identifies specific cancer associations.

## Key findings

- Females with bacterial STIs had higher risks of cervical and colon cancers compared to the general population.
- Males with bacterial STIs showed increased risks of prostate, testicular, and lung cancers.
- Overall cancer risk was elevated in the STI cohort compared to the general population.

## Abstract

We investigated cancer risk among individuals with a prior bacterial sexually transmitted infection (STI) diagnosis using a retrospective cohort study of all Albertan residents diagnosed with chlamydia, gonorrhea, or syphilis during 2000–2014, that was then linked to the Alberta Cancer Registry. Follow‐up started 5 years from their first bacterial STI diagnosis and continued until the first instance of a cancer diagnosis, death, or the study end date (December 31, 2019). Internal comparisons between the bacterial STI groups were undertaken using adjusted hazard ratios, while sex‐specific standardized incidence ratios (SIRs) were calculated to compare cancer risk with the Alberta general population. The likelihood of developing cancer was largely comparable within the bacterial STI cohort, though head/neck cancer was more common after only gonorrhea exposure, and lung cancer was more common after only syphilis exposure. When compared with the general population, statistically significant SIRs were observed among females for cervical cancer (SIR = 1.9, 95%CI = 1.5, 2.3) and thyroid cancer (SIR = 0.8, 95%CI = 0.6, 0.9); females exposed to chlamydia with other STIs, or gonorrhea with other STIs, were also 3.2‐ and 2.9‐times more likely to develop colon cancer, respectively. In males, statistically significantly associations were identified for cancer overall (SIR = 1.1, 95%CI = 1.0, 1.2) and Hodgkin lymphoma (SIR = 1.8, 95%CI = 1.0, 2.9); males exposed to chlamydia only were also 1.5‐ and 1.6‐times more likely to develop prostate and testicular cancer, respectively, while males exposed to only syphilis were 2.4‐times more likely to develop lung cancer. Our findings are consistent with common bacterial STIs being correlates of risk of certain cancers, although the possible etiologic mechanisms may be indirect.

While previous studies have identified the carcinogenicity of viral agents such as HIV, the role of bacterial sexually transmitted infections in carcinogenesis remains understudied despite them similarly causing chronic inflammation. This Canadian study quantified cancer risk following bacterial sexually transmitted infections with chlamydia, gonorrhea, and/or syphilis using population‐based registries. Cancer risk was increased in the infection cohort compared to the general population. Notable excesses occurred for cervical cancer among females, as well as Hodgkin lymphoma, lung cancer, and prostate cancer among males. As bacterial sexually transmitted infection rates rise, the findings highlight how these changes could impact the cancer burden.