Abstract: Objective To establish a highly metastatic model of colorectal cancer in mice by using organ selection of metastasis. Methods Histologically intact C26 colorectal cancer tissues were subcu-taneously implanted into the NOD-SCID mice which is immunodeficiency. In order to gain visible metastatic focus, the tumor bearing mice were undertaken tumor resection in first selection when tumor reached 1.5 cm in diameter. Screening was conducted according to the method of subcutaneous implantation→lung metastasis →subcutaneous inoculation→lung metastasis. Then the same steps were duplicated in BALB/c mice. Tumorgenicity, invasion, metastasis and morphological characteristics of the inplanted tumors were studied by light microscopy, electron microscopy and flow cytometry. Results Highly metastatic models of mice colorectal cancer were obtained after organ screening. After 5 generations in vivo, the carcinoma metastasis rate accounted to 100 percent in NOD-SCID mice, and the metastases of lungs and lymph nodes were noted in all of animals. While only a lower metastasis rate was found when the tumor was subcutaneously implanted in natural mice at the first time. But a 100 percent lung metastatic rate was observed again after being passaged in vivo for 4 generations in natural mice. Conclusions We had established a highly metastasis colorectal cancer model of natural mice which was high, steady, and intuitionistic metastasis and had same biological characteristics of mice colorectal carcinoma. The result provided a useful tool for the study of metastatic mechanism and treatment of human colorectal carcinoma.

Key words: Mice colorectal cancer, Selection, Metastasis, Animal model