A method for separating tumor cells with lymphotropic metastatic potential from those without lymphotropic metastatic potential in a human carcinoma. Cells of the carcinoma are transplanted in each of a plurality of fresh athymic mice. At least one of the athymic mice which does not develop a palpable tumor at the transplant site is treated to suppress the T-cell independent innate anti-tumor activity of natural killer cells therein. Tumor-forming cells at the transplant site of the treated athymic animal are harvested to obtain a cell line of cells with lymphotropic metastatic potential, which is also tested for the expression of T-lymphocyte associated molecules. Such cells are intimately associated with low or diminished angiogenicity and immunogenicity. The traditional scientific criteria for human cancer cells is re-defined, and therapeutic targets for human cancer cells is re-focused.