EFFECTS OF PNEUMOPERITONEUM ON TUMOR IMPLANTATION WITH DECREASING TUMOR INOCULUM

INTRODUCTION: The aim of this study was to determine the effect of pne umoperitoneum on the rate of trocar-site implantation with decreasing inoculum of cancer cells. METHODS: A total of 0.5 mi of GW-39 human co lon cancer cell suspensions at 1 percent (similar to 3.2 x 10(5) cells ) and at 0.5 percent (similar to 1.6 x 10(5) cells; v/v) were injected into the; abdomen of hamsters through a midline incision. Animals in each group were randomized to receive either pneumoperitoneum (1 perce nt = 33; 0.5 percent = 43) or not (1 percent = 32; 0.5 percent = 33) G ross and microscopic tumor implants were documented seven weeks later at four trocar sites. RESULTS: In the 1 percent group, pneumoperitoneu m significantly increased trocar-site tumor implants from 50 to 71 per cent (P < 0.001). Pneumoperitoneum also resulted in the following: 1) more frequent involvement of all four concurrent sites (38 vs. 10 perc ent; P < 0.02); 2) more frequent palpable tumors (13 vs. 5 percent; P < 0.01); 3) larger tumor mass (2.1 +/- 0.6 g vs. 0.2 +/- 0.1 g; P < 0. 02). In the 0.5 percent group, pneumoperitoneum did not significantly increase trocar-site tumor implants, and it did not result in a larger tumor mass. The percent increase in trocar-site implants owing to pne umoperitoneum was influenced by the amount of tumor inoculum (21 perce nt in the 1 percent group; 10 percent in the 0.5 percent group). The m ass of palpable tumor implants after pneumoperitoneum decreased with d ecreased inoculum: I percent = 2.1 +/- 0.6 0.5 percent = 0.3 +/- 0.1 g (P < 0.0001). CONCLUSIONS: Pneumoperitoneum significantly increased b oth tumor implantation rate and mass when similar to 3.2 x 10(5) colon cancer cells were injected into the peritoneal cavity. These effects of pneumoperitoneum diminished with one-half as many tumor cells injec ted in the peritoneal cavity.