Significantly fewer PCNA-positive cells were found in tumours in the ZD6126-treated groups (53% fewer in the weekly group (P<0.01) and 58% fewer in the daily group (P<0.05)), concomitant with significant increases in TUNEL-positive cells in both groups (5.3-fold increase in the weekly group (P<0.007) and 7.4-fold increase in the daily group (P<0.001)). The gene discussed is PCNA; the disease is neoplasm.