We wanted to bring your attention to an open-access publication in which the researchers suggest that the age-related decline of the thymus is more important than DNA mutation as a cancer risk factor.
Repairing the damage
As we have discussed in this article, cancer is caused by DNA damage that creates mutations. Damage to our DNA happens all the time, and we have various repair systems in place for it.
While these systems are efficient, sooner or later, errors happen, and mutations slip through the net nonetheless. Cancer is essentially a game of chance; the more cells and cellular activity there are, the higher the chance a cancerous mutation will appear in one of those cells.
Environmental insults can also influence the chance of DNA damage and thus a potential mutation. Sunlight, harmful molecules in our bodies, radiation, and cellular stress can all influence the risk of damage and possible mutations.
We have cancer safety nets, but these fail as we age
Thankfully, even if a cancerous mutation does happen, we have a variety of systems that work to defend us by destroying these cells. Cells have internal safety systems such as those based on P53, which, upon detecting a cancerous mutation, cause the cell to destroy itself via programmed cell death, which is known as apoptosis.
The immune system is another way we defend ourselves from cancer, and we have a range of immune cells that are designed to seek out and destroy damaged, infected, and cancerous cells. Some of the most important immune cells in this battle against cancer are T cells. These cells are primarily created in the thymus, an immune organ that is located under the breastbone and produces the bulk of the T cells that patrol our bodies.
Unfortunately, as we age, our immune systems become increasingly ineffective and our thymi shrink, changing from T cell-producing tissue to fat. Some researchers believe that this happens due to signals that encourage new tissue to increasingly favor becoming adipose fat tissue over immune cell-producing tissue, and we talk about this in depth here. The end result is that our thymi ultimately lose the ability to produce new T cells, and we become vulnerable to infections, diseases, and cancer.
For this reason, there is a lot of interest in the research community in finding ways to rejuvenate the thymus so that it continues to produce T cells even in an older person. We have interviewed one researcher, Dr. Greg Fahy, about his work on thymic rejuvenation; should you wish to learn more, you can read about that here.
The rejuvenation of the thymus is of huge importance for combating diseases and keeping older people healthy. If the researchers in this paper are correct, and the immune system is more important than DNA mutation when it comes to cancer risk, then the need to rejuvenate the thymus is even more pressing.
The immune system performs a myriad of tasks, from combating invading pathogens and facilitating repair to clearing cellular debris, so it would be no surprise for this to be the case; the sooner we can restore the thymus to working order in older people, the better.
 Sam Palmer, Luca Albergante, Clare C. Blackburn, T. J. Newman (2018). Thymic involution and disease incidence. Proceedings of the National Academy of Sciences Feb 2018, 201714478; DOI: 10.1073/pnas.1714478115