The purpose of this study was to evaluate whether early changes in 3′-deoxy-3′-3H-fluorothymidine (3H-FLT) uptake can reflect the antiproliferative effect of gefitinib in a human tumor xenograft, in comparison with the histopathological markers, Ki-67 and phosphorylated EGFR (phospho-EGFR). Here, EGFR is linked to neoplasm.