Millions of new cancer cases around the world may be caused by infections that can be treated or prevented, suggesting that in some cases cancer can be prevented.
This is the conclusion of a new study published in the journal The Lancet Oncology, which found that approximately one in every outbreak of cancer around the world may be linked to infection, many of which can be prevented through vaccines, medical examinations, or relatively simple treatments.
“We can intervene before the disease develops into cancer,” said study lead author and IARC epidemiologist Gary Clifford.
In 2024, approximately 2.3 million new cancer cases globally will be attributed to infection, equivalent to 12% of all cancer diagnoses.
Two types of infection stood out in particular: Helicobacter pylori, known as H. pylori, which has been mostly associated with stomach cancer, and human papillomavirus (HPV), which has been mainly associated with cervical cancer.
Researchers estimate that these two types of infections will be responsible for more than 1.5 million cancer cases in 2024.
Other types of infections also had a significant impact:
“Some infection-associated cancers, such as liver and stomach cancer, are typically low in survival rates, meaning that a similar proportion of deaths from these cancers are likely attributable to infection,” Harriet Romgay, an epidemiologist at the International Agency for Research on Cancer who co-authored the study, wrote in an email. “For other cancers, including cervical cancer and Kaposi’s sarcoma, infection is a necessary factor for cancer development.”
But she noted that there are highly effective preventive measures for four of the five major infectious causes of cancer, in addition to HIV.
The four infections include human papillomavirus and hepatitis B, for which vaccines are available, in addition to Helicobacter pylori bacteria, and hepatitis C, for which testing and treatment methods are available.
Clifford, Romgay and their colleagues analyzed data from the World Cancer Observatory's Cancer Today database to estimate cancer incidence rates around the world in 2024.
The researchers looked at how many cases of cancer could be caused by certain infections, and then analyzed every pair of infection and cancer type in their data set.
The new analysis builds on previous work published in 2018, but researchers now have a better understanding of the relationships between certain types of infections and cancer.
The new study included 16 additional pairs compared to the previous global analysis from 2018, including some cancers linked to the Epstein-Barr virus.
The new research also reveals that the burden of infection-related cancer is not evenly distributed across the world, with 77% of all cancer cases caused by infection in low- and middle-income countries, reflecting disparities in the prevalence of cancer-causing infections, access to vaccines, and access to early detection services, screenings, and treatments.
“Infection-associated cancers are undoubtedly an important issue in the United States,” said Veronica Federko, a professor of epidemiology at the University of Texas MD Anderson Cancer Center who was not involved in the new study.
She pointed to a separate analysis conducted by the American Cancer Society, which found that 3.4% of all cancer cases among adults aged 30 years and older in 2019, equivalent to about 60,310 cases, were caused by seven infections that were evaluated: Epstein-Barr virus, Helicobacter pylori, hepatitis B, hepatitis C, Kaposi’s sarcoma-associated herpes virus, human immunodeficiency virus, and polyomavirus. Human papilloma.
But she added, "Having a cancer-causing infection does not necessarily mean that a person will develop the disease. This infection increases the risk of certain types of cancer, but the majority of people with the infection will never develop cancer."
She continued: “Cancer usually appears in only a small percentage of people, and this often occurs when the infection continues for many years and coincides with other factors such as age, the efficiency of the immune system, smoking, genetic factors, or other forms of exposure to pathogens.”
Cancer is an extremely complex group of diseases, but new findings show that infections are an area where prevention can make a fundamental difference.
Prevention efforts include vaccination, screening, and treatment of infections that increase the risk of cancer.
For some types of cancer, early screening can also detect changes that precede the development of cancer, allowing them to be treated before the disease develops into metastatic cancer.
For example, individuals can be tested for hepatitis C virus and treated if they are positive, which helps prevent the development of cancer in the future.
“This new research shows us the importance of vaccination and how it can prevent different types of cancer,” Dr. Nancy Liu, a radiation oncologist at Memorial Sloan Kettering Cancer Center who was not involved in the new study, wrote in an email.
She added: "It is no different from receiving the influenza vaccine to prevent illness."
