Routine removal of the thymus during unrelated surgical procedures should be reconsidered in light of a study showing worse health outcomes after thymectomy. All-cause mortality and the risk of cancer were higher among patients who had undergone thymectomy than among controls, and “thymectomy also appeared be associated with an increased risk of autoimmune disease when patients with preoperative infection, cancer, or autoimmune disease were excluded from the analysis,” the authors write. The thymus is needed among younger patients for proper immune development, but its function in adults is unknown.
The study evaluated the risk of death, cancer, and autoimmune disease among adult patients who had undergone thymectomy and in demographically matched controls who had undergone similar cardiothoracic surgery without thymectomy.
“After exclusions, 1,420 patients who had undergone thymectomy and 6021 controls were included in the study; 1,146 of the patients who had undergone thymectomy had a matched control and were included in the primary cohort,” the authors write. “At 5 years after surgery, all-cause mortality was higher in the thymectomy group than in the control group (8.1% vs. 2.8%; relative risk, 2.9; 95% confidence interval [CI], 1.7 to 4.8), as was the risk of cancer (7.4% vs. 3.7%; relative risk, 2.0; 95% CI, 1.3 to 3.2). Although the risk of autoimmune disease did not differ substantially between the groups in the overall primary cohort (relative risk, 1.1; 95% CI, 0.8 to 1.4), a difference was found when patients with preoperative infection, cancer, or autoimmune disease were excluded from the analysis (12.3% vs. 7.9%; relative risk, 1.5; 95% CI, 1.02 to 2.2). In an analysis involving all patients with more than 5 years of follow-up (with or without a matched control), all-cause mortality was higher in the thymectomy group than in the general U.S. population (9.0% vs. 5.2%), as was mortality due to cancer (2.3% vs. 1.5%). In the subgroup of patients in whom T-cell production and plasma cytokine levels were measured (22 in the thymectomy group and 19 in the control group; mean follow-up, 14.2 postoperative years), those who had undergone thymectomy had less new production of CD4+ and CD8+ lymphocytes than controls (mean CD4+ signal joint T-cell receptor excision circle [sjTREC] count, 1451 vs. 526 per microgram of DNA [P=0.009]; mean CD8+ sjTREC count, 1466 vs. 447 per microgram of DNA [P<0.001]) and higher levels of proinflammatory cytokines in the blood.”