Local imbalance of proangiogenic and antiangiogenic factors: a potential mechanism of focal necrosis and dormancy in tumors.

Solid tumors produce both stimulators and inhibitors of angiogenesis. The suppression of metastases by some primary tumors has been attributed to the longer circulatory half-lives of the inhibitors. We propose that intrinsic differences in the physicochemical properties of these regulators may also explain focal suppression of angiogenesis within the primary tumor. We present a mathematical framework that describes production, diffusion, and degradation of these factors in tumor and host tissue and their effect on angiogenesis at local and distal sites. Results show focal suppression of angiogenesis, provide an explanation for tumor dormancy and focal necrosis, and predict a suppressive influence of primary tumors on angiogenesis at metastatic sites. They suggest generally that diffusible factors produced by tumors can stimulate responses in adjacent host tissue, preparing it for further tumor invasion. This study presents a new paradigm for the development of tumor necrosis and offers new insight into angiogenesis regulation and therapy. The framework established for modeling the competing effects of diffusible stimulators and inhibitors can be applied more generally to growth factors/inhibitors and other opposing factors produced in the tumor environment.