Risk of Lymphoma and Leukemia in Thyroid Cancer Patients: A Retrospective Cohort Study in Germany.

Thyroid cancer is the ninth most common cancer worldwide. While differentiated thyroid cancer (DTC) has a high survival rate, concerns arise regarding optimal treatment strategies and potential long-term risks, including second primary malignancies (SPMs), associated with therapies such as radioiodine (RAI). The aim of the present study was to investigate the association between thyroid cancer and the incidence of subsequent lymphoma and leukemia in Germany. This retrospective cohort study used the IQVIA TM Disease Analyzer database and included adults with a first documented diagnosis of thyroid cancer between January 2005 and December 2021 as well as propensity score matched individuals without thyroid cancer in 1284 general practices. Univariate Cox regression models were performed to examine the association between thyroid cancer and the incidence of subsequent lymphoma and leukemia. A total of 4232 thyroid cancer patients (mean age: 54.2 years; 73.6% female) and 21 160 controls (mean age: 54.2 years; 72.6% female) were available for analyses. Thyroid cancer was significantly associated with a higher lymphoma incidence (HR: 3.35, 95% CI: 2.04-5.52), especially in men (HR: 5.37) and those aged 61-70 years. Leukemia incidence was not significantly associated with thyroid cancer (HR: 1.79, 95% CI: 0.91-3.53), although associations were notable in younger age groups. Thyroid cancer is positively associated with a risk of subsequent lymphoma, highlighting the need for vigilant surveillance and tailored treatment strategies. While the association with leukemia is less pronounced, close surveillance remains critical, especially in younger patients.