Most cases of cancer have nothing to do with viruses. But, the role of viruses in cancer is much greater than had been widely believed not very long ago. And, quite a few environmental causes (most famously smoking or crewing tobacco) are know to be significant contributors to cancer rates.
The US Department of Health and Human Services released its 14th Report on Carcinogens today, including seven "newly reviewed" substances, bringing its total number of known human carcinogens to 248.
Five viruses have been added to the list:Human immunodeficiency virus type 1 (HIV-1)Human T-cell lymphotropic virus type 1 (HTLV-1)Epstein-Barr virus (EBV)Kaposi sarcoma-associated herpesvirus (KSHV)Merkel cell polyomavirus (MCV)
These viruses have been linked to more than 20 kinds of cancer, according to the report, including non-melanoma skin cancer, eye cancer, lung cancer, stomach cancer and multiple types of lymphoma.
"Given that approximately 12% of human cancers worldwide are attributed to viruses, and there are no vaccines currently available for these five viruses, prevention strategies to reduce the infections that can lead to cancer are even more critical," said Linda Birnbaum, director of the National Institute of Environmental Health Sciences and the National Toxicology Program, in a statement.From CNN.
The other viruses known to cause cancer are: Hepatitis B, Hepatitis C, and Human Papillomaviruses: Some Genital-Mucosal Types. There are vaccinations available against most strains of these viruses.
There are 240 non-viral substances that are known to cause cancer or strongly linked to cancer.
There are also many known genetic predictors of cancer risk, most famously, the genes that make one vulnerable to breast cancer.
On the other hand, a significant share of all cancers are seemingly random.