About 12% of total cancer cases worldwide in 2024 were likely caused by infection, according to a new study from the World Health Organization (WHO).
The study, published today in The Lancet Oncology, analyzed the frequency and causes of different cancers, looking specifically at the role of infections.
It linked 2.3 million new cases of cancer to infection. Most were caused by just five pathogens: Helicobacter pylori (4%), human papillomavirus or HPV (4%), hepatitis B (2%), Epstein-Barr virus (1%) and hepatitis C (less than 1%). These infections can cause more than 20 different types of cancer, including stomach, liver, blood, and cervical cancers.
So how can an infection cause cancer? And does this mean that these cancers are preventable?
Did we already know this link?
Some authors of the study have been carrying out research in this area for around thirty years. Their previous work looked at cancer cases caused by infections in 1990, 2002, 2008, 2012 and 2018.
The proportion of cancer cases caused by infections appears to have declined over these years (from 18% in 2002), but the authors point out that these comparisons can’t really be made with certainty because the sources and quality of the data have changed over time.
In fact, the latest study didn’t try to compare years. Instead, it aims to highlight areas where infection control and prevention can help reduce cancer rates.
To understand this, it helps to know how infection is linked to cancer. Extensive research has dissected the molecular mechanisms behind this link, and we now know that there are a variety of ways infections can cause cancer.
How can a virus cause cancer?
A virus can (directly or indirectly) change the genes of the cell it infects (the host cell), making that cell more likely to grow out of control and eventually become cancer.
Viruses can act in three main ways.
The first is to disable a cell’s ability to destroy itself (for example, by inactivating the TP53 protein) or to stop dividing (for example, by inactivating the RB protein). A healthy cell would normally try to do these things if infected with a virus.
The second way a virus can cause cancer is by inserting its own DNA into the host cell’s DNA, which can accidentally disrupt genes that control cell death or division (like the ones above).
The third pathway is when the virus itself carries a gene that causes cancer (an oncogene). In many cases, the virus accidentally picked them up from another organism.
The link between viruses and cancer is actually fundamental to modern cancer science and has helped scientists discover the direct link between genetics and cancer that we now take for granted.
What about bacteria and parasites?
It’s not just viruses that cause cancer. Bacterial or parasitic infections – such as Helicobacter pylori (best known for causing stomach ulcers), or Opisthorchis viverrini (a liver fluke, a type of parasitic worm) – can also lead to cancer.
However, these act more indirectly than viruses. Long-term (chronic) infection with these types of organisms can cause significant stress on different tissues.
Inflammation, which is normally part of the body’s immune response, can then become overactive, further damaging tissue.
These stresses can cause carcinogenic damage to the DNA of cells or lead to errors during cell division as the body attempts to quickly produce new cells to repair tissue damage.
In both cases, cells acquire genetic mutations that put them on the path to cancer.
Many cancers are preventable
Of course, there may be other mechanisms linking infections and cancer that we don’t know about, but overall, the link between infections and cancer is indisputable.
What this tells us – and what this new study on rates of cancers caused by infections reinforces – is that many cancers are preventable.
In Australia, one of the best examples of preventing cancers caused by infections is the human papillomavirus (HPV) vaccine.
This vaccine protects against certain strains of HPV strongly associated with cervical cancer and is available to adolescents in Australia.
Since the program launched in 2007, HPV infections have fallen by 90% among those eligible for the vaccine.
Thanks to its success, Australia could be on track to eliminate cervical cancer by 2035.
However, vaccination rates among 15-year-olds fell from 85.7% in 2020 to 79.5% in 2024, which is worrying. As is the case with all vaccines, a high proportion of the population must be vaccinated in order to also protect those who, for health reasons, cannot be vaccinated. For HPV, the WHO and Australia’s objective is to vaccinate 90% of girls aged 15 by 2030.
Unfortunately, the new study also highlights that around 75% of cancers caused by infections were detected in low- and middle-income countries.
Treating infections that can lead to cancer – such as HIV, H. pyloriand hepatitis B and C – is a way to reduce cancer rates. Preventative measures also play a major role, including vaccinations, condoms and disease screening.
However, the availability of these programs in poorer countries may be limited and access therefore remains a major equity issue in the fight against cancer.
The authors would like to acknowledge the contribution of Amali Cooray of the Olivia Newton-John Cancer Research Institute to this article.
John (Eddie) La Marca, Senior Research Officer, Blood Cells and Blood Cancer, WEHI (Walter and Eliza Hall Medical Research Institute) and Sarah Diepstraten, Senior Research Officer, Blood Cell and Blood Cancer Division, WEHI (Walter and Eliza Hall Medical Research Institute)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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