The site of injection of tumor cells in rats does not influence the subsequent distribution of metastases.

Our goal was to examine the influence of circulatory anatomy on the development of metastases. We compared the dissemination of tumor cells to different tissues at different stages in both an orthotopic and a heterotopic model of colon cancer in the rat. We used DHD/K12-PROb cells and two groups of BD-IX rats: group O (orthotopic), in which tumors were implanted by intramural injection of the cecum; and group H (heterotopic), in which cells were injected subcutaneously into the thoracic wall. Animals were assigned randomly to one of nine subgroups of each group in terms of the time between the injection of cells and euthanasia (from the third to the twelfth week). The presence of lung or liver macrometastases was recorded and tumor DNA was detected in lung and liver samples from all animals. We found that lung metastases developed in rats in groups O and H, but no metastases were found in liver parenchymas. The rates of detection of tumor DNA in lung and in liver samples were similar in the two groups. Our results suggest that the site of inoculation of DHD/K12-PROb cells did not influence the pattern of development of metastases. This does not support the proposed role of the circulatory anatomy in the distribution of metastases.