Cancer Risk and Cause-Specific Mortality Among People With Thymoma in the United States

The thymus is essential for T-cell generation and immunity against infections and cancer. However, the health impact of thymoma remains poorly defined, and the implications of thymectomy in this context are unclear.

We used longitudinal data from 17 population-based cancer registries in the United States Surveillance, Epidemiology, and End Results program to identify individuals diagnosed with thymoma from 2000 to 2020. Standardized incidence ratios (SIRs) and standardized mortality ratios (SMRs) were calculated to quantify cancer risk and cause-specific mortality relative to the general population. Multivariable Poisson regression was used to calculate mortality rate ratios (MRRs) comparing mortality rates among patients who received total, partial, or no thymectomy.

Among 3051 individuals with thymoma, the risk was increased for cancer overall (SIR = 1.61, 95% confidence interval [CI]: 1.46-1.78) and for cancers of the lung (SIR = 2.06, 95% CI: 1.60-2.61), soft tissue including the heart (SIR = 5.46, 95% CI: 2.36-11.0), urinary bladder (SIR = 2.13, 95% CI: 1.38-3.14), and thyroid (SIR = 4.03, 95% CI: 2.35-6.46). All-cause mortality was also significantly elevated (SMR = 2.86, 95% CI: 2.70-3.04), with increases noted for deaths due to cancer (SMR = 6.17, 95% CI: 5.67-6.70), infections (SMR = 2.75, 95% CI: 2.04-3.64), chronic obstructive pulmonary disease (SMR = 1.92, 95% CI: 1.39-2.58), and heart disease (SMR = 1.62, 95% CI: 1.37-1.90). Compared with patients with thymoma who did not receive a thymectomy, those who underwent partial or total thymectomy had lower overall mortality (MRR = 0.44, 95% CI: 0.37-0.51, and MRR = 0.35, 95% CI: 0.30-0.41, respectively).

Individuals with thymoma have an elevated risk of subsequent malignancies and increased mortality, particularly from cancer and infections, underscoring the importance of cancer surveillance and infection prevention. Thymectomy is associated with improved mortality, which may reflect a treatment benefit or the effects of patient selection.