Increased rates of pulmonary metastases following sham laparotomy compared to CO2 pneumoperitoneum and the inhibition of metastases utilizing perioperative immunomodulation and a tumor vaccine.

BACKGROUND: Subcutaneous tumor growth and establishment is increased after laparotomy; significantly smaller increases have been noted after CO2pneumoperitoneum (CO2 pneumo). Less is known about the impact of surgery on the fate of blood borne tumor cells. The extent of surgical abdominal wall trauma also correlates with the extent of early postoperative immunosuppression and the inflammatory response. These changes may favor lung metastases (mets) formation. This study's hypotheses were: (a) a reduction in surgical trauma or (b) a perioperative (periop) tumor vaccine or nonspecific immune up-regulation would limit lung mets formation. An intravenous tumor cell injection lung met model was used to test these hypotheses.
METHODS: Study 1 determined the incidence of lung mets after sham laparotomy (OP) and CO2 pneumo. Three groups were studied (n=25/group) : Anesthesia control (AC), CO2 pneumo, and OP. 1 x 105 TA3Haushka adenocarcinoma cells were inoculated via tail vein injection into all mice immediately after surgery. Study 2 determined the impact of perioperative immunomodulation on lung mets formation. Five groups were studied (n=20/group) : AC, OP, OP + Monophosphoryl Lipid A (MPLA), OP + lysed tumor cells (LTC), or OP + MPLA + LTC. The vaccine consisted of 5 x 105 lysed TA3Ha tumor cells (LTC) and was given 5 times preop and once postop to the vaccine groups. MPLA, the nontoxic moiety of lipopolysaccharide, was used both as a vaccine adjuvant in the OP + MPLA + LTC group and as a nonspecific perioperative immune up-regulator in the OP + MPLA group. Five periop injections of MPLA were given to the OP + MPLA group. All mice were given tail vein injections of tumor cells after surgery. Fourteen days after surgery all mice were sacrificed, the lungs transected en bloc, and India ink injected into the trachea. The lungs were placed in Fekete's solution to counterstain the tumor foci white. The number of surface lung metastases was determined by two blinded observers, separately.
RESULTS: In Study 1, there were significantly more lung tumors in the OP group (median=31.5) than the AC group (median=9; p<0.05) or the CO2 Pneumo group (median=6.5; p<0.05). There were no significant differences in the number of metastases between the AC and the CO2 Pneumo groups or in the incidence of animals in each group with 1 or more lung mets. In Study 2 significantly fewer metastases were noted for the Op + LTC group (median=3; p<0.05) and the OP + LTC + MPLA group (median=0; p<0.05) when compared to the OP group (median=20). Although the OP + MPLA group mice had fewer metastases (median=4) than the OP group, this difference was not significant. Significantly fewer of the OP + LTC + MPLA group mice developed one or more lung tumors than in the OP, OP + MPLA, and the OP + LTC groups.
CONCLUSIONS: Full sham laparotomy was associated with more postoperative lung metastases than CO2 pneumo or anesthesia alone in this murine model. Up-regulation of the immune system in the perioperative period with lysed tumor cells, alone or in combination with MPLA, resulted in significantly fewer postoperative lung metastases. MPLA alone resulted in a less marked reduction of lung metastases.