Unsuspected pneumonia detected by increased lung uptake on 111In-ibritumomab tiuxetan scan

99Y-ibritumomab tiuxetan (Zevalin) is a CD20-targeted radioimmunotherapy for the treatment of B-cell non-Hodgkin lymphoma approved by the FDA in 2002. The acquisition of an 111In ibritumomab tiuxetan scan (bioscan) to confirm normal biodistribution before treatment with 99Y-ibritumomab tiuxetan was initially required in the United States until November 2011. This is the first documented example of abnormal biodistribution due to unsuspected pneumonia detected by increased lung uptake on the bioscan. The pneumonia was treated and resolved before 99Y Zevalin, avoiding potential harm and indicating that a screening chest x-ray may be appropriate when a bioscan is not performed.