Ovarian cancer is the fourth most common cause of death in women. Gene therapy using the herpes simplex virus thymidine kinase (HSV-tk) gene followed by ganciclovir (GCV) treatment has been successfully applied in the treatment of different cancers in experimental animals and in humans. In a recent report, we have demonstrated that the HSV-tk/GCV system can be used efficiently to kill human epithelial ovarian cancer cells (Gynecol Obstet Invest 1997;43:268-75). In this work, we wanted to test the ability of the HSV-tk/GCV to treat ovarian cancer in an animal model.The immune-deficient nude mice model was employed, and mice were injected intraperitoneally with the human epithelial ovarian cancer cell line OVCAR3, 10(8) cell/mouse. The mice were divided into three different groups, groups 1 and 2 were treated by intraperitoneal injection of adenovirus carrying the HSV-tk gene (ad-tk) on day 3 after cell implantation. Group 1 received 2 x 10(8) pfu/mouse; group 2 received 20 x 10(8) pfu/mouse. Group 3 did not receive any viral injection and served as our negative control. All mice received GCV 10 mg/kg IP bid for 6 days. All mice were hosted in the same facilities and had access to food and water ad libitum. Mice in group 3 started to show clinical manifestations of disease by day 10, and all mice were dead by day 21 (16 +/- 1.5). At this point mice in groups 1 and 2 appeared perfectly healthy. Autopsy done on group 3 mice demonstrated multiple cancer implants in the abdominal cavity plus hemorrhagic ascitis. In contrast, autopsy on sample mice from groups 1 and 2 at the same time point failed to demonstrate any macroscopic or microscopic cancer.On further follow-up, mice in groups 1 and 2 started to show cancer-related signs, eg, weight loss, movement difficulty, poor reflex response, and finally death. Survival varied between 50 and 101 days with a mean of 66 +/- 17 days for group 1 and 74 +/- 13 days for group 2. Autopsy done on treated mice demonstrated multiple cancer implants and ascitis. In conclusion, a single injection of ad-tk/GCV was able to improve survival in an ovarian cancer mouse model from an average of 16 days to 74 days. Trials with multiple injection in a novel immune-competent mouse model of ovarian cancer are underway in our laboratory.