Incidence, characteristics, and comorbidities of a complete unselected Danish cohort of patients with thymic epithelial tumors.

Background and purpose: We report the incidence, characteristics, and comorbidities of the complete unselected Danish cohort of patients with thymic epitheliums (TETs), which may serve as evidence for guiding treatment, surveillance, and counselling of TET patients.

Patients and methods: All patients diagnosed with TETs from January 1st, 2015, to December 31st, 2020, were identified using the Danish Pathology Data Registry. Data on patient characteristics, comorbidities, and tumor histology were collected from electronic medical records available for all patients.

Results: The cohort consisted of 283 patients with a mean age of 64 years (SD: 12). The crude rate was 8.2/1,000,000 TETs annually, thus higher than the age-standardized rates of 4.8/1,000,000 in the WHO World Standard Population and 6.1/1,000,000 in the European Standard Population. Thymomas were diagnosed in 240 patients (85%) (9% type A, 31% AB, 18% B1, 26% B2, 6% B3, 5% micronodular, 0.4% metaplastic, and 5% of unspecified subtype), thymic carcinomas in 39 patients (14%), and thymic neuroendocrine tumors in 4 patients (1.4%). Tumors in Tumour, Node, Metastasis (TNM) stage I were diagnosed in 181 patients (64%) and were mostly thymomas (72%). Prior to TET diagnosis, 91 (32%) patients presented with autoimmune disorders (19% myasthenia gravis) and 82 patients (29%) had at least one cancer diagnosis.

Interpretation: We found a higher incidence of TETs in Denmark than in previous European population-based studies, while reporting a similar distribution of histological types and tumor stages. Furthermore, we found an increased prevalence of autoimmune disorders and cancers in the cohort before TET diagnosis compared to the general population.