Colon adenocarcinoma and B-16 melanoma grow larger following laparotomy vs. Pneumoperitoneum in a murine model

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Abstract
PURPOSE: Mouse mammary carcinoma tumors are established more easily and grow larger after sham laparotomy and open bowel resection than after CO2 pneumoperitoneum and laparoscopic-assisted bowel resection. The purpose of this study was to determine whether similar differences in tumor growth would be found when sham laparotomy and pneumoperitoneum were compared for the colon-26 mouse adenocarcinoma and B-16 mouse melanoma tumor lines. METHODS: In all three studies, a high-dose injection of tumor cells was used, which resulted in tumors in almost all control mice. In Study 1, female BALB/C mice (n=127) were injected intradermally in the dorsal skin with 106 colon-26 cells in a 0.1-ml volume before interventions. In Study 2, female C57 BL/6 mice (n=140) were inoculated similarly with 106 B-16 melanoma cells. Study 2 consisted of three separate trials conducted on different days. Study 3 was performed because considerable differences in mean tumor size were observed in each of these trials. In Study 3, the B16 experiment was repeated with a larger n (n=82) on a single day. In each study, after tumor cell injections, mice were randomly assigned to one of three groups: 1) anesthesia control (no procedure); 2) full laparotomy (4-cm midline incision × 20 minutes, staple closure); or 3) CO2 pneumoperitoneum (4-6 mmHg × 20 minutes). Tumors were excised and weighed on postoperative day 12. RESULTS: In Studies 1 and 3, mean tumor sizes of the laparotomy groups were significantly larger than both the control group and pneumoperitoneum group lesions (P values by Student's t-test). In Study 2, laparotomy group tumors, although significantly larger than control group lesions, were not significantly larger than pneumoperitoneum group tumors. For all three studies, there was no significant difference between mean tumor sizes of the pneumoperitoneum and control groups. CONCLUSION: Both colon-26 adenocarcinoma and B-16 melanoma tumors grow larger after laparotomy than after pneumoperitoneum in a murine model. The mechanism of these postoperative tumor growth differences remains to be elucidated.