Concomitant resistance (CR), the phenomenon by which tumor-bearing hosts are able to inhibit secondary implants of the same tumor at distant sites of the body, has been previously observed by us and others in different murine tumor models. Here, we verified the generation of CR in nude mice by tumors induced by SC inoculation of Calu-6, a human lung carcinoma cell line. Histological analysis of secondary tumors subject to CR did not reveal macrophage infiltration nor cytotoxic signs. Although serum from tumor-bearing mice inhibited in vitro [3H]thymidine uptake by Calu-6 cells, no significant differences in [3H]thymidine labeling index of tumors implanted in the right flank of mice with and without a primary tumor in the left flank were detected. In our model, the presence of a primary tumor hindered remote tumor angiogenesis, as well as serum from tumor-bearing mice inhibited in vitro proliferation of an endothelial cell line derived from a murine hemangioendothelioma. Conversely, an enhancement of the apoptotic index was observed in secondary tumor implants carried out in tumor-bearing mice. The results reported herein show that human tumor cells are capable of inducing CR, and that this phenomenon would be a consequence of an impaired neovascularization as well as an increased programmed cell death at sites distant from the primary tumor.