AI Scores Thymus Health From Routine CT Scans, Ties Results to Longevity and Cancer Outcomes

Physicians have long treated the thymus as a relic. The small chest organ trains T cells in childhood, then shrinks and is largely forgotten. Two new studies published together in Nature argue that assumption has cost medicine a useful prognostic signal.

<cite index="19-5">The findings, published in two papers in the same issue of Nature, suggest the thymus plays a far more consequential role in adult health than previously understood, and might provide a new target for personalizing disease prevention and cancer treatments.</cite>

The work comes out of the Artificial Intelligence in Medicine Program at Mass General Brigham. <cite index="15-4,15-6">To determine thymic health, the investigators employed a deep-learning framework to analyze routine CT scans. Their AI model was trained on over 5,500 CT images to assess radiographic characteristics of the thymus, including the degree of fatty replacement versus preserved soft tissue, enabling calculation of a personalized "thymic health" score.</cite>

The first study drew from two large prospective cohorts. <cite index="21-7">Researchers developed the deep-learning framework and evaluated its association with longevity and risk of major age-associated diseases in two large prospective cohorts of asymptomatic adults: the National Lung Screening Trial (n = 25,031) and the Framingham Heart Study (n = 2,581).</cite> That is a combined sample north of 27,000 people, which is large enough to take seriously, though both cohorts skew toward adults who agreed to lung or cardiac screening, a selection the authors should address in any follow-on work.

<cite index="14-3">People with healthier thymuses lived longer and had substantially lower risks of heart disease, cancer, and death.</cite> The second paper zeroed in on cancer care. <cite index="21-5">Patients with stronger thymic health had about a 37% lower risk of cancer progression and a 44% lower risk of death, even after accounting for other patient, tumor, and treatment factors.</cite> Those are large effect sizes for a single imaging-derived score, and they warrant caution: observational associations of this magnitude can reflect unmeasured confounders rather than a direct causal pathway through the thymus.

The team did probe one direction of causation. <cite index="15-5">Using data from the prospective TRACERx lung cancer cohort, the researchers found that thymic health correlated with T cell receptor diversity and T cell receptor excision circles, which are indicators of thymic activity and adaptive immune competence.</cite> That biological ladder from imaging score to immune function to outcomes is the mechanistic scaffolding the results need to be interpretable.

Environmental and lifestyle signals showed up in the data as well. <cite index="19-6">Their analysis found that chronic inflammation, smoking, and high body weight were associated with poorer thymic health, suggesting that lifestyle and systemic inflammation may influence immune resilience across the lifespan.</cite>

<cite index="20-4,20-5">For decades, doctors believed the organ was mostly inactive after puberty because it shrinks with age and produces fewer new T cells. As a result, its role in adult health has rarely been examined in large populations.</cite> The new model works from images that hospitals already collect, which is the methodological argument for its potential clinical usefulness: no additional procedure required.

The critical near-term caveat is that there is nothing yet to do with the score. <cite index="15-8">No clinical interventions yet exist for improving thymic health, though there is evidence supporting the development of methods to improve or maintain thymic function during treatment.</cite> Hugo Aerts, the program director and corresponding author on both papers, framed the immediate utility as predictive, not prescriptive, according to a press release reviewed by the Mass General Brigham newsroom: <cite index="19-10">"Improving our understanding and monitoring of thymic health could eventually help physicians better assess disease risk and guide treatment decisions."</cite>

<cite index="19-8,19-9">The team is currently leading additional research to investigate whether other care-associated factors may impact thymic health, including whether unintended radiation exposure to the thymus in patients with lung cancer may affect outcomes.</cite> That last question is clinically consequential: if thoracic radiation incidentally damages thymic tissue in ways that blunt immunotherapy, treatment planning would need to account for it.

Two observational papers, however large, do not settle the biology. Randomized evidence on interventions that improve thymic health, and whether that improvement changes clinical outcomes, is the distance still to travel.

Sources cited:
- Mass General Brigham Newsroom (https://www.massgeneralbrigham.org/en/about/newsroom/press-releases/thymus-critical-to-longevity-and-cancer-treatment)
- Inside Precision Medicine (https://www.insideprecisionmedicine.com/topics/oncology/thymic-health-may-predict-response-to-cancer-immunotherapy/)
- Harvard Gazette (https://news.harvard.edu/gazette/story/2026/03/thymus-may-be-critical-to-adult-health/)
- The Hearty Soul (cohort details) (https://theheartysoul.com/thymus-health-longevity-cancer-immunity-study-2026/)
- ScienceDaily (https://www.sciencedaily.com/releases/2026/06/260601025352.htm)