The thymus gland, integral in childhood immunity, is generally thought to be non-functional in adults. However, recent research suggests this may not be the case, and that the organ might in fact be crucial to our health and cancer prevention as we age.
Once considered a kind of “graveyard” for dying cells and deemed “an evolutionary accident of no very great significance” by Nobel Laureate Sir Peter Medawar, the thymus actually plays a vital role in developing the immune system, producing immune T cells before birth and during childhood.
Despite its significance in our formative years, it was believed the thymus loses functionality in adults, and it is even sometimes removed during cardiac surgery – in a process called thymectomy – to allow access to the heart and major blood vessels. But this often forgotten organ, which is located between the lungs and behind the sternum, might not be as useless as we think.
According to the new study, the thymus may have unexpected importance. When compared to adults who hadn’t had a thymectomy, those that had undergone the surgery had an almost three times higher risk of dying over five years, as well as a heightened risk of developing cancer.
“By studying people who had their thymus removed, we discovered that the thymus is absolutely required for health. If it isn’t there, people’s risk of dying and risk of cancer is at least double,” senior author Dr David T. Scadden said in a statement.
While the study is observational, meaning it cannot prove a causal link between the thymus and adverse patient outcomes, it still has some potentially clinically relevant repercussions.
“[Our findings indicate] that the consequences of thymus removal should be carefully considered when contemplating thymectomy,” Scadden added.
To reach these conclusions, Scadden and co-authors evaluated the risk of death, cancer, and autoimmune disease among 1,146 thymectomy patients and an equal number of adults who underwent cardiothoracic surgery without thymectomy.
Within five years of surgery, the team found, 8.1 percent of patients who had a thymectomy had died, while just 2.8 percent of those who did not have the surgery passed away.
In the same time period, 7.4 percent of thymectomy patients developed cancer, compared to 3.7 percent of controls. Cancers were generally more frequent, varied, and aggressive, with a higher incidence of recurrence and increased mortality when patients received a thymectomy.
In a subgroup of patients, those who had undergone thymectomy had consistently lower production of new T cells and higher levels of pro-inflammatory molecules in the blood.
“Together, these findings support a role for the thymus contributing to new T-cell production in adulthood and to the maintenance of adult human health,” the authors conclude. “The disruption of homeostasis caused by thymectomy is sufficient to adversely affect critical health outcomes, which argues strongly that the adult thymus remains functionally important.”
The study is published in The New England Journal of Medicine.