To investigate the in vivo biodistribution of the contrast agents, following a single i.v. injection of the contrast agents, blood and tissue samples were harvested from SCID mice bearing subcutaneous MDA-MB-231 (EGFR-overexpressing) and U138 MG (non-EGFR-overexpressing) tumor xenografts at different times, and the Gd levels were measured by ICP-MS. This evidence concerns the gene EGFR and neoplasm.