An overlooked organ may a master switch to a longer, healthier life.

While every organ in the human body has a purpose, some serve theirs for only a short time — or so we previously thought.

Now, new research has found that the health of one in particular not only indicates a longer life, but could also be instrumental in fighting off cancer and other deadly illnesses.

For years, there was a widely held belief that our thymus gland — the bowtie-shaped organ located in the upper chest — become essentially inactive once a person hit puberty.

That belief has been shaken up, as researchers from Mass General Brigham looked at findings from two large-scale studies that prove this organ has more to offer in two separate studies.

The first study, published in the journal Nature, used AI to analyze more than 27,000 medical scans from the National Lung Screening Trial and the ongoing Framingham Heart Study.

Adults with a healthy, active thymus live longer and are significantly better at fighting off cancer and heart disease.

While mostly active during childhood, it shrinks after puberty, a process referred to as “thymic decay” by the researchers and which can vary widely between people.

Using the data from the studies, the team looked at the differences in size and composition of the gland and gave patients a thymic health score.

Those who had high, healthy scores had a 50% lower risk of dying prematurely from any cause, a 63% lower risk of death from heart-related issues and a 36% lower risk of developing lung cancer.

But the effects don’t just prevent life-threatening diseases. They can also help those already fighting cancer.

The second study looked at 1,200 patients receiving immunotherapy for several types of cancer.

Those with a healthy thymus had a 37% lower risk of their cancer getting worse and a 44% lower risk of death.

The results of both studies is most likely due to how the organ works.

The thymus plays a critical role in the immune system by training T-cells to fight and kill infections and rogue cancer cells.

And certain lifestyle choices can keep the gland healthy and functioning well into old age.

Factors like smoking, high body weight and constant inflammation were all linked back to poor thymus health.

These findings could be an important piece of the puzzle to discovering better therapies and treatments, as well as prevention methods, for a number of illnesses, according to the researchers.

“The thymus has been overlooked for decades and may be a missing piece in explaining why people age differently, and why cancer treatments fail in some patients,” Hugo Aerts, director of the Artificial Intelligence in Medicine Program at Mass General Brigham, told HealthDay.