Scientists have uncovered a much bigger role for one small organ than previously thought, saying it is vital to the development of children’s immune systems and may also help protect against cancer.
For a long time, this small structure located behind the breastbone was largely dismissed and poorly understood, but new research is changing that view.
The organ is called the thymus, and it naturally becomes smaller over time, shrinking significantly by adulthood and later life.
Because of that decline, many researchers had assumed its importance faded too. New evidence, however, suggests the thymus continues to matter far more than expected.
A study published in Nature indicates that the thymus may influence long-term health and could even help defend the body against disease.
The conclusion came after researchers examined health information from more than 27,000 people involved in both the Framingham Heart Study (FHS) and the National Lung Screening Trial (NLST).
Participants in both studies underwent computed tomography (CT) scans, allowing scientists to assess the size, shape, and makeup of their thymus glands.
Researchers then used AI to evaluate the scans and assign a thymic health score, classifying each organ as low, average, or high in health.
As the data was followed over time, the team found that thymus condition closely matched later health outcomes, even after accounting for factors such as smoking, age, sex, and other health risks.
Those placed in the highest thymic health category had a 50 percent lower relative risk of death 12 years later.
“We suspected the adult thymus might still matter, but we were surprised,” oncologist Hugo Aerts of Harvard University, and director of the Artificial Intelligence in Medicine (AIM) Program at Mass General Brigham, told ScienceAlert.
“We did not expect these differences to be so strongly and consistently associated with longevity, cancer incidence, cardiovascular disease, and cancer therapy response across multiple large, independent cohorts. That suggested the adult thymus is far more important than previously appreciated.”
The findings also showed that people with high thymic health were around 36 percent less likely to develop lung cancer, while their risk of dying from the disease was 50 percent lower than those in the low-health group.
In addition, strong thymus health was associated with a 63 percent lower risk of cardiovascular death in the NLST group, and as much as 92 percent lower in the FHS group.
“These findings change how we think about the immune system in medicine,” Aerts told the outlet. “Our work suggests that thymic health is a fundamental component of that immune fitness and that it can now be measured using routine medical imaging. This opens the possibility of identifying patients who are most likely to benefit from certain therapies, tailoring treatments to preserve immune health, and developing new strategies to maintain immune function as we age.”
Aerts also contributed to another thymus study, which found links between thymic health and better responses to immunotherapy in lung cancer, melanoma, breast cancer, and other diseases.
He said participants with stronger thymus health responded more positively to ‘immunotherapy and survived longer’.
“I’m excited because this is more than the discovery of a new biomarker,” Aerts said. “It suggests that we’ve overlooked a major aspect of human biology for decades. If these findings continue to be confirmed, preserving and measuring immune health could become a new principle of medicine, much like we currently monitor heart or kidney function. The thymus may be one of the first organs that allows us to do that in a practical way.”
Recent complementary research has begun to reveal the biological mechanisms underlying these findings. Scientists have identified specific cellular changes that occur as the thymus ages, including the emergence of nonproductive thymic tissue that accumulates with age. As the thymus shrinks and ages, it produces fewer T cells—the immune system’s specialized cells that identify and destroy infected cells, cancer cells, and other threats.
Additionally, research from the Keck School of Medicine of USC has identified a hormone produced by the thymus called thymulin that helps control age-related inflammation, a condition known as “inflammaging.” As thymulin levels decline with age, inflammatory activity increases, potentially allowing diseases like cancer to progress. In studies with older mice, restoring thymulin levels reduced age-related inflammation, improved cancer survival, and enhanced the effectiveness of cancer immunotherapy. This hormone is believed to play a crucial role in maintaining the body’s ability to fight disease throughout life.
The researchers caution that while the findings are significant, additional studies will be needed to confirm the results, and the imaging technique used to measure thymic health is not yet ready for routine clinical use. Thymic health was also associated with modifiable lifestyle factors including smoking, obesity, and physical activity, though the studies did not determine whether changing these factors can directly improve thymic function.