Contributions of vascularized lymph-node metastases to hematogenous metastasis in a rat mammary carcinoma.

Rats received hind-foot-web (FWI) injections of MT-100-TC mammary carcinoma cells; the resultant tumor metastasized first to the popliteal lymph nodes. Over the course of 4 weeks, in association with increases in tumor weight, the blood-flow to the popliteal nodes increased 18-fold, and their vascular densities increased 2-fold. In spite of this vascularization, cancer cells were detected in only 3 of 648 blood vessels associated with involved, ipsilateral lymph nodes compared with intravascular cells in 82 of 314 vessels associated with "primary" foot-pad lesions. The presence of tumorigenic cancer cells in the right ventricular blood of animals bearing these tumors is, therefore, considered to result from their direct entry into blood vessels from the "primary" lesions, and/or from extra-nodal invasion of vessels in tissues to which nodal tumors were adherent, as distinct from passage via lymphatico-venous communications between tumors and nodal blood-vessels. The reconstructed events occurring in the rat model, with effective restriction of regional node metastases to the nodes themselves for a time, could possibly account for the long-term survival of some patients with breast cancer and regional-node metastases, following surgery.