Wednesday February 12, 2020
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It is known that a viral infection can cause cancer. Researchers at the German Cancer Research Center are investigating which pathogens are responsible for the development of which tumors. Existing relationships can now be named and even numbered.
How often do viruses cause cancer – and under what circumstances? An international team of researchers examined this relationship in a large project. When analyzing more than 2,650 samples from 38 cancers, the scientists found traces of viruses in 13 percent. In these 356 samples, they found the genome of a total of 23 virus types, as the group led by Marc Zapatka and Peter Lichter from the German Cancer Research Center (DKFZ) in Heidelberg reported in the journal “Nature Genetics”. But not all viruses are causally related to the development of tumors.
According to estimates by the World Health Organization (WHO), 15.4 percent of all tumors can be attributed to infections with bacteria, viruses or worms. According to the DKFZ Cancer Information Service, the figure in Germany is around four percent. A total of eleven pathogens are currently considered carcinogenic: This includes above all that stomach bacteria Helicobacter pyloriwhich is responsible for 770,000 cases of gastric cancer worldwide each year. The four next common infections that can lead to tumors are therefore viral:
* Human papilloma viruses (HPV) trigger 640,000 cases worldwide, mainly of cervical cancer, but also of tumors of the throat and throat.
* Hepatitis B (HBV) causes 420,000 cases of liver cancer annually.
* Hepatitis C (HCV) is associated with 170,000 liver cancer cases per year
* The herpes virus Epstein-Barr virus (EBV) is considered to trigger 120,000 tumor diseases per year, mainly lymphomas.
Overall, the WHO assumes that around 10 percent of all tumors worldwide are caused by viral infections. The team around Zapatka and Lichter has now analyzed this connection. It is not only about identifying cancer-causing viruses, but also about clarifying the mechanisms by which an infection can lead to a tumor. In general, according to Lichter, more than the 10 percent of tumors estimated by the WHO seem to be caused by viruses. “Our percentage is slightly higher.”
Mutation caused by viruses or the body’s own virus defense
The team found HPV variant 16 in the genome in 19 out of 20 samples of cervical cancer and in 18 out of 57 cases of neck / throat tumors. Hepatitis B DNA occurred in 62 of a total of 330 cases of liver cancer. Traces of the Epstein-Barr virus appeared in 5.5 percent of the cancer samples.
For papilloma viruses and hepatitis B, the analyzes showed that the incorporation of the virus genome into human DNA can lead to mutations. This appears to be the most common mechanism for viral tumorigenesis. Sometimes, however, the cell’s own virus defense, which is directed against the pathogen, can cause mutations with serious consequences.
The analysis should also help clarify when an infection causes cancer and when not. For example, the Epstein-Barr virus is common to more than 90 percent of Europeans – but only a few of them develop a tumor. The relationships should now be analyzed in more detail.
“So far we have not been able to confirm the frequently voiced assumption that other, previously unknown viruses are associated with cancer,” says study leader Lichter. “In many cases, however, we can now see more clearly how the pathogens cause cells to malignant.”
Prevention possible through vaccination
“The question of which viruses are linked to cancer is highly relevant for medicine”, first author Zapatka is quoted in a DKFZ message. Real prevention is possible for virus-related cancers. Once a cancer-causing virus has been identified, there is a chance that vaccination can prevent the infection and thus prevent cancer from developing.
An example of this is HPV vaccination for girls and young women, which is now also recommended for boys and young men. The DKFZ is currently researching a vaccine against the Epstein-Barr virus.
However, infection with one of these viruses does not necessarily lead to cancer: “Only a fraction of the people infected with tumor-promoting viruses actually develop a corresponding tumor, and this usually takes decades,” emphasizes the Cancer Information Service. “Although the viruses play a more or less important role in the development of some types of cancer, the virus infection is never the only trigger for cancer.”
The Cancer Information Service also explicitly emphasizes: “Cancer itself is not contagious, not even the types of tumor that can be triggered by viruses.” The current study is part of the “Pan-Cancer Analysis of Whole Genome” (PCAWG). In this consortium, around 1,300 researchers want to clarify which genetic changes play a role in the development of cancer.
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