Effect of the Extent of Thymus Excision on the Risk of Subsequent Cancer Development

OBJECTIVES: Thymus removal can alter immune function and potentially influence cancer development. However, the relationship between the extent of thymus removal and postoperative cancer development remains underexplored. This study aimed to identify risk factors for cancer development post-thymectomy, with particular focus on the extent of thymic resection. METHODS: We reviewed 254 patients who underwent thymectomy between 2005 and 2021. Patients with myasthenia gravis, combined resection of adjacent organs, thymic cancer, or tumour recurrence were excluded. Clinical characteristics and postoperative cancer incidence were compared between the total and partial thymectomy groups. RESULTS: This study included 112 patients: 91 (81%) and 21 (19%) in the total and partial thymectomy groups, respectively. Patients in the total thymectomy group were significantly older than those in the partial thymectomy group (median age, 60 vs 44 years; P = .021). No significant differences were observed in sex, smoking history, preoperative cancer history, or observation period between the groups. Postoperative cancer development was significantly more common in the total thymectomy group (21 [23.1%] vs 1 [4.8%], P = .032). The median interval between surgery and cancer development was 2367 days. In the multivariable analysis, total thymectomy was identified as an independent risk factor for cancer development (hazard ratio 6.26, P = .032) after adjusting for potential confounders (age, sex, surgical method, and smoking history). CONCLUSIONS: Total thymectomy was identified as the only independent factor associated with increased postoperative cancer risk. These findings suggest the need to consider the extent of thymectomy and long-term cancer surveillance post-surgery. IRB INFORMATION: Institutional Review Board of Kitasato University (approval number: B24-079). The need to obtain written informed consent from each patient was waived because the study was retrospective.