PARP1 and neoplasm: Notably, tumor uptake at 2 h in a U87 subcutaneous model was reported as 0.17% ID/g (tumor: muscle = ~4.36) whereas in the U251 orthotopic model it was 0.43% ID/g (tumor: muscle = 13.7 ± 4.1) despite the same PARP1 expression levels in both U87 and U251 tissues.