CEACAM5 and neoplasm: Biodistribution studies in CEA-positive tumor-bearing mice revealed that the 111In-labeled I253A fragment with the slowest blood clearance (serum half-life: 27.7 h) had the highest tumor uptake (44.6 percentage injected dose per gram of tissue [%ID/g] at 24 h p.i.), whereas the radiometal-labeled H310A/H435Q fragment with the most rapid elimination (serum half-life: 7.1 h) only had a maximum tumor uptake of 28.0%ID/g at 12 h p.i. The H310A fragment which has an intermediate serum half-life exhibited an intermediate level of tumor uptake.