About 2.3 million new cases of cancer identified worldwide in 2024 were linked to viral, bacterial, and parasitic infections. This accounts for approximately 12% of all new cancer cases — effectively one in eight. The majority of these diseases are attributed to just five infectious agents. As reported by the International Agency for Research on Cancer (IARC), part of the World Health Organization, the new study provides the most comprehensive picture to date of the global burden of cancer related to infections. The researchers' work was published in *The Lancet Oncology*. They analyzed data from 2024 and assessed the contribution of 12 infectious agents to the development of various types of cancer. ### Five Infections — Over 2 Million Cases It turned out that the overwhelming majority of infection-related cancer cases were due to just five pathogens. The leading one was the bacterium **Helicobacter pylori**, which can live in the human stomach for long periods and contribute to the development of peptic ulcers and stomach cancer. Researchers linked it to about **760,000 cancer cases** in a year. Nearly as many — about **750,000 cases** — were attributed to the human papillomavirus (**HPV**). It is one of the main causes of cervical cancer and can also be associated with certain types of oropharyngeal, anal, and genital cancers. Another approximately **360,000 cases** were linked to the hepatitis B virus. The Epstein-Barr virus was associated with around **260,000 cases**, while the hepatitis C virus was linked to about **160,000**. Together, these five infectious agents accounted for nearly all cases of cancer that researchers classified as infection-related. ### Poor Countries Suffer the Most The distribution of such diseases across the globe was extremely uneven. Countries with low and middle income accounted for about **77% of all infection-related cancer cases**. The burden is particularly high in East Asia: about **990,000 such cases** were reported here, or approximately 42% of the global total. The main causes were *Helicobacter pylori* and the hepatitis B virus. However, the highest proportion of infection-related tumors was noted in countries in Sub-Saharan Africa. There, infections are linked to about **one in four cancer cases**. Researchers attribute this disparity, in part, to unequal access to vaccination, diagnostics, screening, and timely treatment. ### This Does Not Mean Cancer Is Contagious The authors of the study emphasize an important distinction: **cancer itself is not an infectious disease and is not transmitted from person to person in the usual way**. Certain viruses, bacteria, or parasites can be transmitted, which may increase the likelihood of tumor development after years — and sometimes decades. The mechanisms vary. Some infections cause chronic inflammation, others alter cell function or affect the immune system. As a result, with prolonged infection, the likelihood of malignant changes may increase. However, infection with *Helicobacter pylori*, HPV, or the Epstein-Barr virus does not mean that a person will necessarily develop cancer. Most infected individuals do not develop the disease. ### Some of These Cases Can Be Prevented The main conclusion of the study is that infection-related cancer offers additional opportunities for prevention. Vaccines exist against HPV and hepatitis B. Hepatitis C can now often be successfully treated with antiviral medications. *Helicobacter pylori* can be detected and eradicated with appropriate therapy. Screening and early detection of precancerous changes — especially in cervical cancer — also play an additional role. Therefore, reducing the prevalence of certain infections can simultaneously decrease the number of cancer cases. ### The Number of Cancer Cases Will Increase Significantly The issue gains additional significance against the backdrop of the overall rise in cancer cases. According to WHO estimates, about **20 million new cancer cases** were registered worldwide in 2024. Due to aging and population growth, this figure is expected to increase significantly in the coming decades. That is why scientists consider the fight against infections one of the most practical directions for cancer prevention. New data reveal a paradoxical picture: millions of cases of one of humanity's most severe diseases begin with infections, some of which medicine already has vaccines, diagnostics, or effective treatments for. Therefore, expanding access to these measures could be one way to genuinely reduce the future global cancer burden.
