Higher colon cancer tumor proliferative index and lower tumor cell death rate in mice undergoing laparotomy versus insufflation.

BACKGROUND: Our laboratory has previously shown that tumors are established more easily and grow larger after laparotomy than after laparoscopy. To characterize these differences in tumor growth further, the tumor cell death rates and tumor proliferation rates were compared in vivo after full sham laparotomy versus carbon dioxide (CO2) insufflation.
METHODS: Female Balb/C mice (n = 36) were inoculated intradermally in the dorsal skin with 106 C-26 colon adenocarcinoma cells in 0.1 ml of culture media no more than 1 h before interventions. The mice then were randomized to one of three groups: anesthesia control, CO2 insufflation, or sham laparotomy. The anesthesia control group underwent no procedure. The insufflation group underwent CO2 pneumoperitoneum (4-6 mmHg) for 20 min via a 20-gauge angiocatheter. The laparotomy group underwent a midline incision from xiphoid to pubis, which was closed after 20 min. Tumors were excised from half the mice in each group on postoperative day 7, and from the remaining mice on postoperative day 14. Sections of tumors were made then stained separately for free 3? hydroxyl ends of genomic deoxyribonucleic acid (DNA) using fluorescein-deoxyunidine triphosphate (dUTP), and immunohistochemically for proliferating cell nuclear antigen (PCNA). Apoptosis was measured by quantitating DNA strand breaks in individual cells using fluorescence microscopy. Fluorescein-positive cells in five random high-power fields (x200) were counted in a blinded fashion. The proliferative index of each tumor was determined by averaging PCNA positive cells in five high-power fields (x450) counted in a blinded fashion with the aid of an optical grid.
RESULTS: On postoperative day 7, there was no significant difference in the proliferative index or apoptotic rates among the three groups. On postoperative day 14, the proliferative index in the laparotomy group was significantly higher than in either the insufflation or control group (p < 0.001). The proliferative index in the insufflation group also was significantly higher than in the control group (p < 0.05). Inverse differences in apoptotic rates were found. The apoptotic rate in the laparotomy group was significantly lower than in either the insufflation (p < 0.05) or control group (p < 0.001). The apoptotic rate in the insufflation group was significantly lower than in the control group (p < 0.001).
CONCLUSIONS: We have demonstrated that there is a significantly higher rate of tumor cell proliferation and a significantly lower rate of tumor cell death with the C-26 colon adenocarcinoma tumor line after laparotomy than after insufflation or anesthesia alone on post-operative day 14. The mechanisms of these phenomena are unclear. It appears that certain factors postoperatively stimulate tumors to proliferate at a higher rate, causing tumor cells to die at a lower rate in the laparotomy group than in the insufflation group.