SULF1 and neoplasm: We used the transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) method to detect apoptotic cells and found that the percentage of apoptotic tumor cells in the Ad5-hSulf1 group was significantly higher than in the Ad5-EGFP control group or the blank control group (P < 0.001; Figure 4D).