Thus, in the present study, to determine whether early changes in 3H-FLT uptake can reflect the antiproliferative effect of gefitinib, we determined the changes in 3HFLT uptake level after the start of treatment at different doses of gefitinib in comparison with those in 18F-FDG uptake, Ki-67 expression, and phospho-EGFR levels in a human tumor xenograft (EGFR-dependent human tumor xenograft model, A431). This evidence concerns the gene EGFR and neoplasm.