Can infections lead to cancer?

Scientific recognition of the connection between infections and cancer has risen remarkably since the beginning of the 21st century.(1) Although previous investigations first linked H. pylori infection to gastric cancer over four decades ago, the association between these phenomena appeared limited and unclear.(2) The latent period between carcinogenic infections and cancer can span decades, which substantially complicates researchers’ efforts to evaluate causality and the efficacy of control strategies.(1) That said, epidemiological survey data that has accumulated over time now decisively validates the causative role of chronic infections in cancer. According to one assessment, 2.2 million new cancer cases traced their origin to infections in 2018, which equals 13% of the world’s cancer burden. The distribution of carcinogenic infections varies vastly by geographic locale, with such disease being highest among populations of developing countries in East Asia and Sub-Saharan Africa.(3) These disparities in prevalence arise from a combination of factors, most notably deficits in medical infrastructure, public sanitation, and vaccine availability.(3,4)

Of the 11 biological agents identified as group 1 carcinogens by the International Agency for Research on Cancer (IARC), 4 account for upwards of 90% of infection-mediated cancers: H. pylori, high-risk human papillomavirus (HPV), hepatitis B virus (HBV), and hepatitis C virus (HCV).(4) Both men and women equally share the burden of infection-mediated cancers, but causative pathogens vary markedly by sex:

Table 1: Estimated numbers of infection-attributable cancer cases in 2018, by infectious pathogen, cancer subsite, and biological gender. Adapted from de Martel, et al. (2018):