• "Spontaneous" lung metastases develop in over 50% of the animals bearing subcutaneous isografts of WB-2054, a rat colon carcinoma. A metastatic variant has been developed by "Fidler" type in vivo selection, yielding 100% lung metastasis. In a five-week assay to test the organ specificity of this lung metastatic variant, however, "experimental" liver and lung metastases could be induced in 100% and 60% of animals on portal venous and intravenous injections, respectively. The results demonstrate selection of a metastatic variant from heterogeneous primary tumor, and suggest at least two interacting mechanisms: (1) mechanical (the anatomy of the bloodborne metastatic pathways) and (2) biologic (factors intrinsic to primary tumor subpopulations that can be selected for metastatic proclivity). In addition, liver metastases were successfully established from colon tumors induced by cecal wall injection of tumor cells. Such a spontaneous liver metastasis model will be useful to study the specific mechanisms involved during metastasis of colon cancer to the liver.
(Arch Surg 1989;124:49-54)