Thymic hyperplasia after mRNA based Covid-19 vaccination.

Reactive lymphadenopathy with increased 18F-Fluordeoxyglucose uptake in positron emission tomography/computed tomography scans is known after mRNA vaccination (BNT162B2, mRNA-1273) against severe acute respiratory syndrome coronavirus type 2. Besides this, increased 18F-Fluordeoxyglucose uptake in the thymus might occur after mRNA vaccination as shown in our case of a young patient with mantle cell lymphoma. Especially in patients with lymphoma but also in other patients with cancer it is critical to distinguish between immune responses and involvement of the disease to avoid inadequate treatment decisions.