Medical Mythbusting Commentary for June 18, 2026

Source:
A ‘Useless’ Organ That Doctors Often Remove May Actually Fight Cancer

Reference:
The Thymus: Function and the Debate Over Its Removal

The thymus is a small organ located behind the breastbone, in front of the heart. It serves as the “training ground” for T cells — the immune system’s soldiers that fight infections, destroy cancer cells, and prevent the body from attacking itself. [1-2] During childhood, the thymus is highly active, producing a diverse army of T cells. With age, the thymus gradually shrinks (a process called involution), leading to the long-held assumption that it becomes essentially useless in adults. [1][3] Because of its location, surgeons have routinely removed it during heart and chest surgeries, treating it as expendable tissue. [3]

The Landmark 2023 NEJM Study (Kooshesh et al.)

A pivotal 2023 study published in the New England Journal of Medicine challenged this assumption. Kooshesh and colleagues compared over 1,100 adults who had their thymus removed during cardiothoracic surgery to matched controls who had similar surgery without thymectomy. [4] The findings were striking:

• All-cause mortality was nearly 3-fold higher in the thymectomy group at 5 years (8.1% vs. 2.8%). [4]
• Cancer risk was doubled (7.4% vs. 3.7%), and cancers were more aggressive and recurrent. [4]
• Autoimmune disease risk was modestly elevated (relative risk 1.5) when patients with pre-existing conditions were excluded. [4]
• Immunologically, thymectomy patients had dramatically reduced new T-cell production and elevated proinflammatory cytokines even 14 years after surgery. [4]

Figure 1. Effect of Thymectomy on Long-Term Mortality.

Health Consequences of Thymus Removal in Adults. N Engl J Med. August 2, 2023.

Used under license from The New England Journal of Medicine.

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Studies That Did Not Confirm These Findings

Several subsequent studies have produced conflicting results, particularly in specific populations:

• A 2026 study by Hanson et al. in the European Journal of Cardio-Thoracic Surgery found that the incidence of new cancers after thymectomy (0.87 cases/100 person-years) was comparable to the general U.S. population (0.81 cases/100 person-years), though autoimmune disease rates were higher. [5]
• Resio et al. (2025) analyzed large U.S. databases (NCDB and SEER) of patients who underwent thymectomy for localized thymoma and found no increased 5-year mortality or cancer death compared to the general population or propensity-matched surgical controls. [6]
• Khateb et al. (2026) studied myasthenia gravis patients specifically and found no difference in extrathymic cancer incidence between thymectomized and non-thymectomized patients after adjusting for confounders. [7]
• Tsirkin et al. (2024) found that for myasthenia gravis patients, the benefits of thymectomy outweighed potential risks, with zero deaths and zero post-thymectomy cancers in the MG-thymectomy group. [8]

A New Dimension: Thymic “Health” as a Biomarker

A 2026 study in Nature by Bernatz et al. used deep learning to quantify thymic health from routine chest imaging in over 27,000 adults. Higher thymic health was associated with lower all-cause mortality, reduced lung cancer incidence, and lower cardiovascular mortality, reinforcing the idea that the thymus remains a central regulator of immune-mediated aging even without surgical removal. [9]

Where the Evidence Stands

The debate remains unresolved. The original NEJM study was retrospective and observational, and its authors acknowledged it cannot establish causation. [4] Critics have noted concerns about confounding, cancer types (many were skin cancers), and the lack of an MG-specific population. [2][7] A key emerging distinction is that total thymectomy may carry greater risk than partial resection — one Japanese study found total thymectomy was the only independent risk factor for subsequent cancer development (HR 6.26). [10] Meanwhile, for patients with myasthenia gravis or thymic tumors, thymectomy remains clearly beneficial and should not be withheld based on these concerns. [2][8] The consensus is that incidental or unnecessary thymectomy should be avoided when possible. [8]

In short, the thymus appears to be far more important in adulthood than previously believed, but the clinical consequences of its removal likely depend on the patient population, the extent of resection, and the indication for surgery.