The Incidence of Malignancy and Autoimmune Disorders After Thymectomy: An Exploratory Study

Thymectomy reportedly increases the risk of cancer, autoimmune disease, and death. Studies are few and data limited. We sought to determine the incidence of postoperative malignancy and autoimmune disease in patients who underwent thymectomy.

We conducted a retrospective review of adult patients undergoing thymectomy between 2008 and 2020. Postoperative cancers and autoimmune disease were diagnosed after thymectomy. Incidence rates were calculated using patient-years and compared to the National Cancer Institute's (NCI) Surveillance, Epidemiology, and End Results (SEER) programme incidence of cancer for the US general population. Autoimmune disease rates were compared to previously published results.

There were 226 patients with a median age of 55 years (interquartile range [IQR] = 39-67), mostly female (129, 57%) and non-smokers (132, 58%). At baseline, 117 (52%) had autoimmune disease, including 102 (45%) with myasthenia gravis. Eighty-four (37%) thymomas were identified. Median follow-up was 6.0 years (134 with >5-year follow-up and 44 with >10-year follow-up). We observed 13 (6%) new malignancies for an incidence of 0.87 cases/100 person-years (0.87%) and comparable to the NCI rate of 0.81 cases/100 person-years (0.81%). Incident cancers developed within the first 5 years after surgery at 0.92 cases/100 person-years (0.92%) or 4.6% cumulatively over 5 years, compared to NCI data at 4%. There were 19 (8%) new autoimmune diagnoses with an incidence rate of 1.3 cases/100 person-years (1.3%) and is higher than large population studies (0.7 cases/100 person-years for all ages).

Development of new cancers following thymectomy in the United States is similar to the general population. But we identified a higher incidence of autoimmune disease, matching prior studies.