Lymphatic metastasis of mammary adenocarcinoma. An experimental study in the rat with a brief review of the literature.

When 5 million cells of the solid form 13762 rat mammary carcinoma are implanted into the footpad of syngeneic rats there is consistent (approximately 100%) metastasis to the draining popliteal node and thence up the lymphatic chain to the lungs. With the transmission electron microscope tumor cells are seen to penetrate gaps in the lymphatic endothelium, probably but not certainly, between endothelial cells. There is neither widespread patency nor significant destruction of lymphatic endothelium. The tumor cells penetrate in groups and lie in the lymphatic in groups with some evidence of acinar differentiation. Tumor cells lodge in groups in the subcapsular sinus and progressively pass down the radial sinusoids and destroy the node; as they grow there is extensive differentiation into adenocarcinoma. The draining lymph obtained by cannulation does not contain an increase in total cells. A few tumor cells are present mostly in clumps. Recruitment is continuous but not progressively increasing. Any theories on neoplastic invasion and metastasis must take into consideration possible aggregation of some tumor cell types in groups. The literature on experimental lymphatic metastasis is reviewed briefly.