Does keeping your thymus mean less cancer and autoimmune disease?
Conflicting. Of 6 studies that test it, 3 agree, 2 disagree and 1 partly agrees.
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The claim checked: People who keep their thymus have less cancer and less autoimmune diseaseHear it at 59:16
What do the studies say?
Conflicting
The thymus is a small organ in the chest that trains immune cells. It shrinks with age. Three of six studies agree. In a lung-screening trial, people whose CT scans showed a healthier thymus got lung cancer less often: 3.4% against 5.3% over 6 years. In Boston, people who had the thymus removed got cancer more often within 5 years, 7.4% against 3.7%. Two studies disagree: in Toronto and in Israel, removal made no difference to later cancer. One is mixed.
Computed from 6 studies that test this point, each judged by two readers, in full.
Sources land on both sides.
6 more studies are waiting for a full read and do not count yet.
“People who had an intact thymus tended to have less diseases such as autoimmune disease in and cancer. People who lost their thymus as they grew older, because the thymus naturally involutes and dies, tended to have more.”
The study behind the claimThe retelling overstates it
What did the study actually test?
On tape: someone at Harvard used AI to read CT scans of thousands of people, and an intact thymus went with less autoimmune disease and less cancer; he calls it correlative, not causal. This study matches the AI, CT, Harvard (Mass General Brigham AIM program), size and correlative details. It found lower lung cancer incidence (HR 0.64, high vs low thymic health) and lower cancer mortality, but only in older heavy smokers in the NLST. It did not measure autoimmune disease: autoimmunity is in the text only as a cited reference title. The authors' discussion widens the result to 'disease incidence, including cancer' and 'disease-agnostic relevance', and also says the design does not allow conclusions about causality. The NEJM 2023 thymectomy cohort (37530823, same Harvard hospital group, no AI or CT) is the likely source of the autoimmune half. It found more cancer after thymectomy (RR 2.0), and more autoimmune disease only after people with disease before surgery were excluded (RR 1.5). No errata found for 41851466.
Thymic health consequences in adults.Nature, 2026. Retrospective secondary analysis of two prospective cohorts; a deep learning model scores thymic health on routine chest CT, then Cox models for death and disease over up to 12 years, 27,612 adults: 25,031 in the National Lung Screening Trial (aged 55 to 74 with at least 30 pack-years of smoking) and 2,581 in the Framingham Heart Study CT cohort.
What was saidWhat the study did
What was given
MatchesAn intact thymus seen by AI on CT scansA deep learning thymic health score from routine chest CT, top 25% and middle 50% against the bottom 25%
Compared with
MatchesPeople who lost their thymus as they grew olderPeople in the bottom 25% of thymic health
What was measured
DiffersAutoimmune disease and cancerLung cancer incidence, lung cancer and cancer-specific mortality, cardiovascular and all-cause mortality; no autoimmune outcome
Who took part
DiffersThousands of people across thousands of disease states25,031 older heavy smokers (NLST) for the cancer results; 2,581 Framingham adults for cardiovascular mortality
What it found
“Participants with high and average thymic health were less likely to develop lung cancer than participants with low thymic health (high versus low thymic health: 3.4% versus 5.3% Kaplan–Meier incidence estimate at 6 years; HR 0.64; 95% CI 0.53–0.76; average versus low thymic health: 4.1% versus 5.3%; HR 0.78; 95% CI 0.67–0.90; Fig. 3a ).”
“Our results show that thymic decay in adults is highly individualized and that loss of thymic health increases mortality and disease incidence, including cancer and cardiovascular diseases.”
NIH (NCI, NHLBI, NIA and NIDCR grants, including U24CA194354, R35CA22052 and R01AG067457), European Research Council, DFG, Lundbeck Foundation, Novo Nordisk Foundation and others; the Framingham Heart Study is funded by an NHLBI contract. Competing interests: one author (M.J.-H.) has consulted for Astex and Achilles Therapeutics and received speaker fees from Pfizer, Bristol Myers Squibb and Genentech; the other authors declare none. Two readers agreed on the label, and the paper was read in full.
Point 1 of 2Conflicting
Adults who keep an intact or larger thymus have a lower risk of cancer than adults whose thymus has shrunk away
Agree 3
other primary study · 2026 · landmark · cited on tape
“Participants with high and average thymic health were less likely to develop lung cancer than participants with low thymic health (high versus low thymic health: 3.4% versus 5.3% Kaplan–Meier incidence estimate at 6 years; HR 0.64; 95% CI 0.53–0.76; average versus low thymic health: 4.1% versus 5.3%; HR 0.78; 95% CI 0.67–0.90; Fig. 3a ).”
Thymic health consequences in adults. Nature Who: asymptomatic adults with chest CT in the National Lung Screening Trial (older heavy smokers) and the Framingham Heart Study; thymic health scored by a deep learning model on CT
PMID 41851466
other primary study · 2023 · landmark
“Patients who had undergone thymectomy were more likely than controls to have cancer within 5 years after surgery (7.4% vs. 3.7%; relative risk, 2.0; 95% CI, 1.3 to 3.2); the results were robust to the exclusion of patients with preoperative myasthenia gravis, patients with preoperative thymoma, or patients with preoperative cancer, as well as to the exclusion of all patients with preoperative infection, cancer, or autoimmune disease (Fig. 2A).”
Health Consequences of Thymus Removal in Adults. N Engl J Med Who: adults who had thymectomy at Massachusetts General Hospital (1993-2020) vs. age-, race- and sex-matched adults who had cardiothoracic surgery without thymectomy; immunology subgroup of 22 thymectomy patients and 19 controls
PMID 37530823
other primary study · 2026
“In conclusion, this study provides the first clinical evidence that HCC occurrence is associated with reduced CT-derived thymic dimensions in patients with compensated viral cirrhosis.”
Radiographic evidence of thymic involution in hepatocellular carcinoma: a propensity score-matched study in viral cirrhosis. Front Immunol Who: adults aged 18-75 with compensated (Child-Pugh A) hepatitis B/C cirrhosis at one Kunming, China hospital (2016-2022), with vs. without resectable hepatocellular carcinoma, thymus measured on chest CT
PMID 42729300
Partly agree 1
other primary study · 2025
“Conversely, within the MG cohort, in which we have recently showed an increased incidence of extrathymic cancers ( 12 ), thymectomy was not linked to higher mortality rates or increased prevalences of cancer or autoimmune diseases when compared to the surgical control groups.”
Survival and autoimmune risks post-thymectomy. Front Immunol Who: patients at Rambam Medical Center, Israel (2010-2023): myasthenia gravis with thymectomy, myasthenia gravis without thymectomy, non-myasthenic thymectomy (mostly thymic tumors), and thoracoscopy with thymus left intact
PMID 40181957
Disagree 2
other primary study · 2026
“Cox models in both matched and IPTW models showed no relationship between thymectomy and extrathymic malignancy, HR: 0.94, 95% CI: 0.83–1.07, and HR: 1.22, 95% CI: 0.55–2.7, respectively.”
The Effect of Thymectomy on the Incidence of Extrathymic Cancers and Autoimmune Diseases in Patients With Non-Thymomatous Myasthenia Gravis. Muscle Nerve Who: adults with non-thymomatous myasthenia gravis followed at the Toronto General Hospital neuromuscular clinic (2000-2025), with vs. without thymectomy; thymoma patients excluded
PMID 41862279
other primary study · 2026
“The observed 10‐year incidence of malignancy was identical in the matched thymectomy and control groups (4.3%; n = 17 in each group).”
Long-Term Cancer and Mortality After Thymectomy. Eur J Neurol Who: adults (>=18) who had thymectomy at Rambam Health Care Campus, Israel (1986-2025) vs. age- and sex-matched adults who had CABG and/or valve surgery without thymectomy (2004-2025)
PMID 42538851
Point 2 of 2Leaning for
Adults who keep an intact or larger thymus have a lower risk of autoimmune disease
Only one of eight studies agrees. In Taiwan, autoimmune disease was 2.68 times as common after the thymus was removed. One disagrees: an Israeli study found no difference over 10 years. Six are mixed. In the Boston study, the higher risk faded when people were followed for 20 years. The CT study described on the episode did not measure autoimmune disease.
Computed from 8 studies that test this point, each judged by two readers, in full.
7 more studies are waiting for a full read and do not count yet.
Agree 1
other primary study · 2020
“In this study, the overall incidence rate of any type ADs was 2.68 times higher in the Txd cohort than in the non‐Txd cohort, with an aHR of 2.65 after adjustment for age and sex.”
Risk of incident autoimmune diseases in patients with thymectomy. Ann Clin Transl Neurol Who: Taiwan National Health Insurance beneficiaries (2002-2015), thymectomized patients with and without myasthenia gravis vs. age- and sex-frequency-matched non-thymectomized patients with and without MG; mean age about 47, 59% women
PMID 32478484
Partly agree 6
other primary study · 2025
“In comparison to healthy controls, the autoimmune disease patients had a larger bilobed thymus, with increases observed in the predominant sides, including length, thickness, transverse diameter, and anteroposterior diameter ( Fig. 1 , Table 1 ).”
Thymic characteristics in patients with autoimmune diseases: a multicentre radiological observational study. Lancet Reg Health West Pac Who: patients with 16 autoimmune diseases (SLE, Sjogren's, MS, RA, Hashimoto's, MG, NMOSD and others) and age- and sex-matched healthy controls from 5 tertiary hospitals in China, chest CT 2020-2023; 76% women, mean age about 52.7
PMID 40677849
other primary study · 2023 · landmark
“Because this difference dissipated when risk was evaluated over a 20-year period, thymectomy appeared to have transiently and modestly increased the risk of autoimmune disease.”
Health Consequences of Thymus Removal in Adults. N Engl J Med Who: adults who had thymectomy at Massachusetts General Hospital (1993-2020) vs. age-, race- and sex-matched adults who had cardiothoracic surgery without thymectomy
PMID 37530823
other primary study · 2017
“Our study, that was strictly designed to include only adults without evidence of thymic activity upon thymus removal in infancy, revealed no increase of clinical/subclinical manifestations of allergy or of autoimmune diseases, as compared with a group of age matched healthy individuals.”
Autoimmunity and allergy control in adults submitted to complete thymectomy early in infancy. PLoS One Who: young adults in Portugal (median age 24) who had complete thymectomy in early infancy during cardiac surgery, with no residual thymic activity by sjTREC, vs. age-matched healthy controls
PMID 28686710
other primary study · 2025
“Post thymectomy, three non-MG patients developed new autoimmune disease versus none in the MG-Thy cohort, which did not result in clinical significance (p=0.16).”
Survival and autoimmune risks post-thymectomy. Front Immunol Who: patients at Rambam Medical Center, Israel (2010-2023): myasthenia gravis with thymectomy, myasthenia gravis without thymectomy, non-myasthenic thymectomy (mostly thymic tumors), and thoracoscopy with thymus left intact
PMID 40181957
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other primary study · 2023
“In conclusion, we observed a higher prevalence rate of autoimmune diseases, especially rheumatoid arthritis, in MG patients after thymectomy.”
Clinical characteristics of myasthenia gravis (MG) patients developing other autoimmune diseases after thymectomy from one single center cohort. Thorac Cancer Who: consecutive myasthenia gravis patients who had thymectomy at Beijing Hospital, China (2012-2021); mean age at operation 47; 29.7% thymoma
PMID 36419347
other primary study · 2026
“Regarding autoimmune disorders, we had conflicting results, with a small but statistically significant increased risk in the thymectomy group in the matched cohort, but no statistically significant difference in the IPWT model.”
The Effect of Thymectomy on the Incidence of Extrathymic Cancers and Autoimmune Diseases in Patients With Non-Thymomatous Myasthenia Gravis. Muscle Nerve Who: adults with non-thymomatous myasthenia gravis followed at the Toronto General Hospital neuromuscular clinic (2000-2025), with vs. without thymectomy; thymoma patients excluded
PMID 41862279
Disagree 1
other primary study · 2026
“We observed no difference in incident immune‐related disease between cohorts over 10 years, including after exclusion of post‐thymectomy MG diagnoses.”
Long-Term Cancer and Mortality After Thymectomy. Eur J Neurol Who: adults (>=18) who had thymectomy at Rambam Health Care Campus, Israel (1986-2025) vs. age- and sex-matched adults who had CABG and/or valve surgery without thymectomy (2004-2025)
PMID 42538851