ICAM1 and neoplasm: Possible explanations for this lack of radiation-induced effect may include: (1) a change in affinity for its target after conjugation and labelling of the ICAM-1 antibody, (2) an increase in ICAM-1 expression in the untreated PSN-1 cells after growth as a xenograft in inoculated mice, or (3) interference in the in vivo ICAM-1 signal caused by murine ICAM-1 expressed by the host (which may be altered by the presence of the xenograft tumour).