Infections are a preventable cause of cancer, according to a new study in The Lancet Oncology. Researchers led by the International Agency for Research on Cancer estimated that 2.3 million new cancer cases worldwide in 2024 were attributable to infections.

That equals 12 per cent of all cancer cases. The authors said the findings highlight the importance of infection control in cancer prevention, noting that some prevention measures exist and should be better implemented.

Pathogens Behind the Burden

The team used 2024 data from the Global Cancer Observatory to estimate cases tied to 12 pathogens classified as group 1 carcinogens. They include Helicobacter pylori (H. pylori), human papillomavirus (HPV), hepatitis B and C, Epstein-Barr virus and HIV.

Most cases traced to five pathogens. H. pylori and HPV each accounted for 4 per cent of cancers, followed by hepatitis B at 2 per cent, Epstein-Barr virus at 1 per cent and hepatitis C at less than 1 per cent.

The infections can lead to more than 20 types of cancer, including stomach, liver, blood and cervical cancers. A separate analysis of 2022 data from 27 countries found that, on average, about 70 per cent of gastric cancer cases were attributable to H. pylori.

How Infections Trigger Cancer

Viruses can directly or indirectly change the genes of the cells they infect, making those cells more likely to grow out of control. Research has found three main ways.

A virus may switch off a cell's ability to destroy itself or stop dividing, such as by inactivating the TP53 or RB proteins. It may insert its own DNA into the host cell's DNA, disrupting genes that control cell death or division.

A third route involves viruses that carry oncogenes, genes that can promote uncontrolled cell growth. Some viral oncogenes originated from cellular genes captured by viruses, while others are encoded by the virus itself. Bacteria and parasites, such as H. pylori, work more indirectly.

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Long-term infection with these organisms stresses tissues and can make inflammation overactive. The resulting DNA damage or cell-division errors can leave cells with mutations that set them on the road towards cancer.

Vaccines, Treatment and Screening

Vaccines exist for HPV and hepatitis B and have been shown to reduce cancer. The study urges development of new vaccines for other agents, including Epstein-Barr virus, H. pylori and Kaposi's sarcoma-associated herpesvirus.

Since Australia's HPV vaccine programme began in 2007, HPV infections have dropped by 90 per cent among people eligible for the vaccine. The country could be on track to eliminate cervical cancer by 2035.

Vaccination rates among Australian 15-year-olds have slipped from 85.7 per cent in 2020 to 79.5 per cent in 2024. The WHO target is to vaccinate 90 per cent of girls against HPV, while Australia's target extends to both girls and boys.

Treating infections that can lead to cancer, such as HIV, H. pylori and hepatitis B and C, is another way to lower cancer rates. Vaccination, condoms and disease screening also play a major role.

A review of prevention strategies calls the Pap test, introduced in 1928, the oldest example of early cancer diagnosis. HPV DNA testing was later added to cervical screening.

Japan and South Korea run national gastric cancer screening programmes that include endoscopy to detect the disease at an early stage. Some virus-driven cancers can take 15 to 40 years to develop after infection.

In chronic hepatitis B, antiviral treatment can slow the progression of liver disease and reduce the risk of liver cancer. Older clinical trials of lamivudine also found reduced disease progression and hepatocellular carcinoma among patients with advanced fibrosis or cirrhosis.

Cirrhosis is present in about 70 to 90 per cent of people with hepatocellular carcinoma at diagnosis.

About 77 per cent of infection-related cancers occurred in low- and middle-income countries, where access to vaccination, treatment and screening can be limited.

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