Nothing surprises me, I’m a scientist.”
-Indiana Jones
In 2019, the world was introduced to a brand new pathogen, the SARS-CoV2 coronavirus, that caused a brand new, and very odd disease, COVID-19. Between then and now, your humble bloggeur has penned 153 blog posts, many of which focused on how strange the disease is and describing our learning process as we figured it out on the fly. Many of these posts were necessarily equivocal because we simply did not have enough information to make firm conclusions on how the virus affects different people. Over time, we learned how to better treat the disease, and that learning curve continues. It was necessary to end many blog posts with the weak statement, “We will see.” Well we are still seeing and learning about this odd malady that consists of a melody of symptoms across myriad organs.
Research is now beginning to reveal a possible link between CoV-2 infection and cancer. As before, these observations are preliminary and will be further scrutinized, but they are bolstered by the discovery of a possible mechanism that could explain how the CoV-2 virus might cause cancer.
We know of many different viruses that cause cancer in animals. We also have a good understanding of how the viruses do that. There also are a few viruses, but not many, that cause human cancer, and we also mostly understand how they exert their oncogenic effects. These human cancer viruses include human papilloma virus (HPV), which causes cervical, and head and neck cancers. Hepatitis B virus can lead to liver cancer. Human T cell leukemia virus causes leukemia, and Epstein Barr virus can lead to lymphoma and a few other types of cancers. And so on.
To date, there has been very little association between any coronaviruses and cancer in animals or humans. But, that might be changing.
Several recent papers have revealed a genetic link between COVID-19 and cancer. One paper showed that people with an increased genetic risk of COVID-19, were also at increased genetic risk of developing endometrial cancer. The limitation of this study is that it cannot distinguish between a correlated high risk of COVID and cancer, vs whether COVID causes the cancer. It is the old conundrum of discerning between correlation vs cause-and-effect.
A second study incrementally advanced the above findings. Using a low resolution genetic mapping technique called genome-wide association, it found a positive correlation (there is that “C” word again) between people genetically predisposed to both severe COVID and increased risk for endometrial cancer. While still a correlation, one would predict that if there was a cause-and-effect relationship between COVID and cancer, that the risks for both would be similar. This is what the study showed.
Finally, a third study uncovered a possible mechanism by which SARS-CoV-2 could cause cancer. Having a possible mechanism in hand bolsters the possibility that the theoretical link between COVID and cancer is true. But first, a little back story about cancer genetics.
Cancer genetics. Basically, cancer is a genetic disease. That does not necessarily mean that it is always inherited. Most cancers probably are not. But, when the genetic fidelity of a cell messes up, it can become immortal, can grow in an unregulated fashion, and can become resistant to normal signals that should cause it to die. In a nutshell, that is cancer. Generally speaking, there are two kinds of genes that contribute to this process. 1) Dominant acting oncogenes are aberrant genes that when expressed, drive the above activities. 2) Suppressor genes provide brakes to the above activities, and when absent, the brake is released. In both cases, genetic abnormalities either activate oncogenes to drive cell immortality and growth, or eliminate expression or activity of tumor suppressor genes removing the brakes to cell growth. Usually, cancer is a stepwise process in which cells sequentially accumulate different abnormal oncogenes and suppressor genes. The combination of which leads to full blown cancer.
One of the first tumor suppressor genes to be identified is called P53. In several different tumors, it was noticed that expression of this gene was missing due to DNA mutation. Further research showed that when expressed, P53 provides a brake on cell growth. There are many ways that P53 can be inactivated. Genetic mutation can prevent its expression, or hinder its function. We also know that a few viruses that cause cancer in people, like hepatitis B virus and Epstein-Barr virus, produce proteins that can interact with and inactivate the P53 gene product. A paper published in November, now reports that two CoV-2 proteins interact with cellular proteins to stimulate complex pathways that lead to degradation of the P53 gene product, releasing the anti-cancer brake in infected cells. The research also shows that that P53 activity is lost in patients with severe COVID disease but not in those with less severe illness. P53 loss also correlates with length of COVID symptoms. In other words, the more severe the COVID disease, the greater the chance that the P53 brake is lost.
This observation does not yet prove that inhibition of P53 by the CoV-2 virus causes cancer, but it now presents an important hypothesis that will be given much research attention. Questions remain regarding the association between CoV-2 infection and cancer. Also, since COVID infections are generally relatively short-lived, how long does the loss of P53 function last? Are long-COVID patients at increased risk for chronic loss of P53 and cancer? Is this loss of function sufficient to launch the multistep pathway that leads to cancer?
Once again, we will see.