(CNN) — Millions of new cancer cases around the world may be caused by infections that are either treatable or preventable, suggesting that the cancer could have been avoided altogether.
That’s according to new research published in the journal The Lancet Oncology, which found that roughly 1 in 8 cancer cases around the world may be linked to infections – many of which can be prevented through vaccines, screening or relatively straightforward treatments.
“We can intervene before it gets anywhere near cancer,” said Gary Clifford, the study’s senior author and an epidemiologist at the International Agency for Research on Cancer.
“We just need the politics and the finances and the buy-in from the public and the communication to get the programs implemented. Prevention works,” Clifford said. “It’s an awareness-raising issue.”
About 2.3 million new cancer cases were attributable to infections globally in 2024, which is equivalent to 12% of all cancer diagnoses, the new study found. And two infections stood out in particular: Helicobacter pylori, commonly known as H. pylori, which was mostly associated with gastric cancers and human papillomavirus, or HPV, which was predominantly associated with cervical cancer. Together, researchers estimate that these two infections accounted for more than 1.5 million cancer cases in 2024.
Other infections contributed substantially as well:
- Hepatitis B or HBV was linked to an estimated 360,000 cancer cases, which were mostly liver cancers.
- The Epstein-Barr virus or EBV was associated with about 260,000 cancer cases, of which a head and neck cancer starting in the nasopharynx was the main driver.
- Hepatitis C or HCV was tied to 160,000 cancer cases, mostly liver cancers.
“Some infection-related cancers, such as liver and gastric cancer, generally have poor prognosis, meaning that a similar proportion of deaths from these cancers are likely attributable to infection. For other cancers, including cervical cancer and Kaposi sarcoma, infection is necessary for cancer development,” Harriet Rumgay, epidemiologist at the International Agency for Research on Cancer and an author of the study, said in an email.
“However, highly effective prevention measures already exist for four of the five leading infectious causes of cancer, as well as for HIV,” Rumgay said, referring to the human immunodeficiency virus. The four infections include HPV and hepatitis B, for which vaccines are available, as well as H. pylori and hepatitis C, for which testing and treatments are available.
Clifford, Rumgay and their colleagues analyzed data from the Global Cancer Observatory’s Cancer Today database to estimate the incidence of cancer around the world in 2024. They examined how many of those cancer cases could be attributable to infections and then analyzed each infection-cancer pair in their data set.
The new analysis builds on earlier work published in 2018, but the researchers now have a better understanding of the relationships between certain infections and cancer. The new study incorporated 16 additional infection-cancer pairs compared with the previous 2018 global analysis, including some cancers paired with EBV.
“EBV is one of these agents for which we knew it was related to some cancers. In fact, EBV was the first ever cancer-causing agent of infection to be discovered in Burkitt lymphoma,” Clifford said.
“That was like 60 years ago almost, and that was the first realization that a virus could cause cancer. And since then, we’ve identified it in other cancers, particularly nasopharyngeal carcinomas,” he said. “We were already clear about the link with EBV, even back in that 2018 data. So, it was there, but it wasn’t really fully addressed because we didn’t understand the full extent of the cancer burden that it was causing.”
Where the infection-related cancer burden is greatest
The new research also reveals that the burden of infection-related cancers isn’t evenly distributed around the world. Low-income and middle-income countries accounted for 77% of all infection-attributable cancer cases, reflecting differences in the prevalence of cancer-causing infections as well as access to vaccines, screening, testing and treatment.
But if health officials know which infections are contributing to cancer, and where those infections are most common, they can focus resources on the strategies that have the potential to save lives.
“Even within the United States, the burden of infection-related cancer is not evenly distributed, and some populations have higher rates of infections such as hepatitis B, hepatitis C, HPV or H. pylori, while others have less access to vaccination, screening or treatment. And these differences can translate into disparities in cancer incidence many years later,” said Veronika Fedirko, professor of epidemiology at The University of Texas MD Anderson Cancer Center in Houston, who was not involved in the new study.
“Infection-related cancers are certainly an important issue in the United States,” she said, referring to a separate analysis from the American Cancer Society that found in 2019, 3.4% of all cancers among adults 30 and older – which was about 60,310 cases – were attributable to seven infections evaluated: EBV, H. pylori, hepatitis B, hepatitis C, Kaposi sarcoma-associated herpesvirus, HIV and, the largest contributor, HPV.
“Having a cancer-causing infection does not mean that a person will develop cancer. These infections increase the risk of certain cancers, but most people who are infected will never develop cancer,” Fedirko said. “Cancer usually develops only in a small proportion of people, often when an infection persists for many years and together with other factors such as age, immune function, smoking, genetics or other exposures.”
How to ‘take away’ the risk
Cancer is an enormously complicated group of diseases with many different causes and risk factors, including genetics, environmental exposures, aging and lifestyle factors. But the new findings show that infections represent an area where prevention can make a meaningful difference.
Prevention efforts can include vaccination and, when appropriate, testing for and treating infections that increase cancer risk. For some cancers, screening can also identify precancerous changes so they can be treated before invasive cancer develops.
Getting tested and following up with a doctor “almost takes away any cancer risk,” Clifford said.
Once infections get diagnosed, “we know how to manage them,” he said. “The large majority of these infections will not cause cancer. Some of them will, and we’re learning more about which ones, but that’s a work in progress. The point is: It doesn’t mean that you’ve got a cancer just because you have the infection.”
For instance, people can be screened for hepatitis C and treated if they are infected, thus helping to prevent cancer from developing down the road.
The same is true for H. pylori. The bacterium is relatively common, and many people who carry it may not immediately realize they have an infection. But H. pylori can cause chronic inflammation in the stomach and become a major risk factor for stomach cancer. Treating the infection with antibiotics can reduce that risk, giving doctors another opportunity to intervene before cancer may develop.
Additionally, HPV and hepatitis B are examples of how vaccination can help prevent cancer. Hepatitis B infection can damage the liver over time and increase the risk of liver cancer, but there is a vaccine available that can help prevent the viral infection.
HPV is a group of more than 200 related viruses, which can spread through sexual contact. In some cases, HPV infection can lead to six types of cancer: cervical, anal, penile, vaginal, vulvar and oropharyngeal (mouth and throat). But the vaccine can protect against those cancers since it works by preventing HPV infection.
The new research “teaches us the importance of vaccination and how that can prevent different types of cancer,” Dr. Nancy Lee, a radiation oncologist at Memorial Sloan Kettering Cancer Center who was not involved in the new study, said in an email.
“This is no different than getting your flu shot to prevent the flu. The public needs to be made aware and vaccination should be reinforced,” Lee said. “Many different types of cancers are caused by infection and if we prevent the infection, the incidence of cancer should be lower.”
Other prevention measures that reduce transmission of various cancer-attributable infections include “safe injection practices, condom use, and HIV pre-exposure prophylaxis,” Rumgay said. “If implemented widely and equitably, these strategies could prevent hundreds of thousands, if not millions, of future cancer cases worldwide.”
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