News Health & Medicine The thymus withers away after puberty. But it may be important for adults Removing the thymus is associated with higher rates of death and cancer, a new study finds The thymus (orange in this illustration) is an immune system organ that sits between the lungs, right in front of and above the heart. This gland might be more important for adult health than previously thought, a new study suggests. janulla/iStock/Getty Images Plus Share this:EmailFacebookTwitterPinterestPocketRedditPrint By McKenzie Prillaman August 2, 2023 at 5:00 pm A mysterious organ that’s most active in childhood might play a previously underappreciated role in adults.