Infection

While infections (bacteria, viruses, parasites) are responsible for an estimated 12% of new cancer cases annually worldwide, they cause more than one-quarter of all cancers in many low-income countries in Africa and Asia (Map 5.1).

The five most important cancer-causing infectious agents are Helicobacter pylori (850,000 cases globally), human papillomavirus (HPV) (730,000), hepatitis B virus (HBV) (380,000), hepatitis C virus (HCV) (170,000), and Epstein-Barr virus (EBV) (200,000) (Figure 5.1).

Human papillomavirus, Helicobacter pylori, and Hepatitis B and C viruses cause more than 90% of all infection-related cancers worldwide.

The contribution of each infectious agent to cancer burden varies substantially across different regions (Figure 5.2).

Helicobacter pylori causes 90% of stomach cancers, the majority of which occur in Eastern Asia. HPV infection is a necessary cause of cervical cancer, the leading cause of cancer death among women in many low-income countries, and is also responsible for a substantial proportion of anal, vulvar, vaginal, penile, and head and neck cancers (Figure 5.3).

Worldwide, HBV and HCV infections account for 55% and 21% of liver cancer deaths, respectively, with HBV tending to be the predominant cause of liver cancer in less developed countries and HCV in more developed settings. EBV causes lymphomas, nasopharyngeal carcinoma, and 7% of stomach cancer. Other cancer-causing infections include Kaposi sarcoma-associated herpesvirus (HHV-8; 42,000 cases, mainly in sub-Saharan Africa), human T-cell lymphotropic virus, Merkel cell virus, liver flukes, and Schistosoma haematobium. Human immunodeficiency virus (HIV) also indirectly causes infection-related cancers through immunosuppression and is estimated, for example, to be responsible for 20% of cervical cancer and 80% of Kaposi sarcoma in sub-Saharan Africa.