Pulmonary tumor colony formation following i.v. inoculation of six human colorectal carcinoma xenografts in young gnotobiotic athymic mice.

The lung colonizing potential of 6 xenografted human colorectal adenocarcinomas following tail vein inoculation of tumor cell suspensions into gnotobiotic 3-4-week-old congenitally athymic mice was investigated. One of the lines, CRCo2, was of particular interest, as apparently distinctive lung colonizing phenotypes, large (greater than 2.5 mm diameter) and small (less than 1 mm diameter) colonies were identified, and variant lines with greater, equal, or lesser ability to grow in the lungs relative to the sc tumor of origin were observed. Another line, CRCo1, was also able to grow well in the lungs following tail vein inoculation, but subsequent cycles of lung tumor recovery and reinoculation i.v. did not result in an enhancement of the tumor's lung colonizing ability relative to the initial i.v. inoculation of the sc carried tumor. Scattered lung colonies were observed following i.v. inoculation of sc carried xenografts in three of the four other lines, but we could not consistently recover lung colonies with these tumors. The data are in accord with the clinical observation that pulmonary metastasis is not a high frequency event in human colorectal carcinoma, illustrating the selective nature and experimental utility of this model of metastasis. Further, there were indications of the inefficient and/or random nature of the metastatic process in some of the tumors, while in others, evidence for both effectively higher and lower metastatic variants were found, as might be predicted in heterogeneous tumor cell populations.