Pathogenesis and characteristics of spontaneously metastasizing mammary carcinomas and the general principle of metastasis.

Chemical mammary carcinogenesis in immunologically attennuated W/Fu female rats, subjected to specific and nonspecific immunostimulations, yielded many spontaneously metastasizing adenocarcinomas with varying degrees of glandular differentiation, and growth rates. The pathogenesis of these tumors suggested that while carcinogens transform target cells, the host immune system endows them with metastatic potential. The metastatic pathways were recognizable as hematogenous, lymphogenous, or hematogenous-lymphogenous combined, according to the capacity of the tumor cells to intravasate the lymphatic and/or vascular channel and traverse the pulmonary artery. The same metastatic pattern can be reproduced with cells from any of the organs involved, indicating that it is inherent in all cells within a given tumor, rather than being determined by the organs they colonize. The biological, biochemical and immunological characteristics of these tumors resemble human breast cancer thus becoming an effective tool in the formulation of the general principle of metastasis by malignant solid tumors.