Infections cause one in eight cancers worldwide
WHO study links more than two million cases in 2024 to five pathogens, vaccines or cures already exist for four of the five
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New research from the World Health Organisation analysed the frequency and causes of different cancers (AFP via Getty)
AFP via Getty
Infections from bacteria or parasites can lead to cancer (Getty/iStock)
Getty/iStock
Roughly one in eight of the world's cancer cases in 2024 was caused by an infection rather than by smoking, diet or alcohol, according to new research from the World Health Organisation published in The Lancet Oncology. The analysis links 2.3 million new cancer cases to pathogens, and traces most of them to just five: Helicobacter pylori, human papillomavirus, hepatitis B, Epstein-Barr virus and hepatitis C. Together they are implicated in more than twenty types of cancer, including stomach, liver, blood and cervical cancers.
HPV and H. pylori each account for about four per cent of all cases, hepatitis B two per cent, Epstein-Barr one per cent and hepatitis C under one per cent. The mechanisms vary. A virus can switch off a cell's ability to destroy itself by inactivating the TP53 protein, or to stop dividing by disabling RB; it can insert its own DNA into the host genome and disrupt the genes that police cell death and division; or it can carry an oncogene, often one picked up by accident from another organism. Bacteria and parasites such as H. pylori and the liver fluke Opisthorchis viverrini work more slowly, through chronic infection, overactive inflammation and the DNA mistakes that accumulate as tissue repairs itself. The authors describe the connection as indisputable, and note that further mechanisms may yet be undiscovered.
The study's authors, some of whom have spent around thirty years on the question, have run comparable analyses in 1990, 2002, 2008, 2012 and 2018. The infection share appears to have fallen from a high of eighteen per cent in 2002, but they caution that the years cannot be honestly compared: the sources and quality of the data have changed too much. The stated purpose of the new figure is not to chart progress but to show where preventing infection would prevent cancer.
HPV accounts for about four per cent of all cancers — the same share as H. pylori — and vaccines against it already exist. Four of the five pathogens on the list have a vaccine or a cure; Epstein-Barr virus is the exception.