By Crystal Phend

Thymectomy carried a substantially increased risk of all-cause mortality and cancer for adults, a "landmark" study showed.

Adults who had undergone thymectomy had at least double the risk of all-cause mortality and cancer at 5 years post-surgery compared with matched patients who had undergone cardiothoracic surgery without thymectomy:

All-cause mortality: 8.1% vs 2.8% (relative risk [RR] 2.9, 95% CI 1.7-4.8)

Cancer: 7.4% vs 3.7% (RR 2.0, 95% CI 1.3-3.2)

Autoimmune disease did not differ substantially between groups overall, reported David T. Scadden, MD, of the Center for Regenerative Medicine at Massachusetts General Hospital in Boston, and colleagues.

But after excluding patients with potentially confounding conditions (preoperative infection, cancer, or pre-existing autoimmune disease), autoimmune disease was a relative 50% more common after thymectomy (12.3% vs 7.9%; RR 1.5, 95% CI 1.02-2.2).

Even when comparing unmatched thymectomy patients to the general population, all-cause mortality was higher in the thymectomy group (9.0% vs 5.2%), as was mortality due to cancer (2.3% vs 1.5%).

Incidental thymectomy is common during cardiothoracic surgery due to the pyramid-shaped organ's location in the chest in front of the heart where surgeons need to access the surgical field.

While the thymus plays a critical role in normal immune system development, it was thought to be safe to remove in adulthood, "particularly since the thymus naturally involutes with age," the researchers noted.

Their conclusion from the study was that the thymus continues to be functionally important for human health in adulthood.

In an accompanying editorial, Naomi Taylor, MD, PhD, of the National Cancer Institute Pediatric Oncology Branch in Bethesda, Maryland, called the research a "landmark" study with "important repercussions for the care of patients undergoing cardiothoracic surgery and strongly argues against total thymectomy if it can be avoided."

Prior studies had shown that the adult thymus continues to produce T lymphocytes, under both pathologic and physiologic conditions, and this study supports an important role of that function, she noted.

"[I]t is remarkable that the possibility that thymectomy would lead to detrimental effects in adults without underlying pathologic conditions was only studied in depth 25 years later," she added.

The study used the Mass General Brigham Research Patient Data Registry to identify all 1,420 adults who had thymectomy at Massachusetts General Hospital from January 1993 to March 2020. Patients who died within 90 days after the procedure or who had nonlaparoscopic cardiac surgery within 5 years after the procedure were excluded.