Viruses and Cancer

Larry A. Law

Infections caused by a virus are responsible for 10-20% of cancers worldwide. "Treating virus-induced cancers with standard cancer therapies can help shrink tumors, but it doesn't fix the underlying problem of the virus," said Dr. Jun Zhao. Dr. Zhao works at the Cleveland Clinic and he authored a study which uncovered one of the mechanisms that the Kaposi sarcoma-associated herpesvirus (KSHV) uses to induce cancer. The study was published in the journal Nature Communications.

Compromised Immune Systems

​KSHV is similar to other herpesviruses and stays dormant in the body after primary infection. However, when the immune system becomes weakened or compromised, as it does in many elderly people, transplant recipients, or those with acquired immunodeficiency syndrome (AIDS), the virus can reactivate. In these immunocompromised individuals, the reactivated virus "can trigger aggressive cancers."

​A key observation that bears pointing out is that a healthy immune system gets rid of viruses daily and/or keeps them in a dormant state where they cannot damage healthy cells. It is only when our defensive system is down, that the virus can get a foothold. Cancer can be prevented by maintaining a healthy immune system—that is an important take-away—we are not victims of our genes nor the microbes that might invade our bodies.

Viral Mechanism Discovered

Most viruses don't produce their own energy or the molecules they need to reproduce. They have to hijack the body's cells to do the work for them. Researchers discovered that the KSHV virus took control of two host proteins (CDK6 and CAD) which allowed the virus to replicate more quickly and the cells to multiply and spread out of control. This makes KSHV-induced cancers very "fast-acting, aggressive, and difficult to treat." The research team discovered that the combination of Palbociclib—a drug that is FDA-approved to treat breast cancer and which works by blocking CDK6—and a compound that blocks CAD (the two host proteins that are hijacked by the virus) caused a substantial reduction in tumor size and improvements in cancer survival rates in preclinical models. “Most tumors virtually disappeared after about a month of treatment, and remaining tumors shrank around 80%.”
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It is estimated that 10% of Europeans and Americans have KSHV while the number of people in Africa could be as high as 50%. A University of Pittsburgh article stated, "It is highly likely that over 95% of persons who are healthy and infected with KSHV do not have symptoms and never will." Problems only develop once a person's immune system becomes compromised. 

Viruses Capable of Causing Cancer

According to the American Cancer Society, the following viruses can cause cancer in humans:

Human papillomaviruses
Epstein-Barr virus
Hepatitis B and C viruses
Human immunodeficiency virus (HIV)
Human T-lymphotropic virus-1
Merkel cell polyomavirus

The American Society of Microbiology states, "Viruses can lead to cancer by associating with host proteins, proliferating when the human immune system is weakened, and hijacking proliferating human cells. Compared to other viruses, human tumor viruses are unusual because they infect, but do not kill, their host cells." This process allows the human tumor viruses to initiate ongoing infections. Again, maintaining a healthy immune system is the key to healthy living. For more information on how to do that, see my book.