Implications of Immune-Mediated Metastatic Growth on Metastatic Dormancy, Blow-Up, Early Detection, and Treatment
Metastatic seeding of distant organs can occur in the very early stages of primary tumor development. Once seeded, these micrometastases may enter a dormant phase that can last decades. Curiously, the surgical removal of the primary tumor can stimulate the accelerated growth of distant metastases, a phenomenon known as metastatic blow-up. Although several theories have been proposed to explain metastatic dormancy and blow-up, most mathematical investigations have ignored the important pro-tumor effects of the immune system. In this work, we address that shortcoming by developing an ordinary differential equation model of the immune-mediated theory of metastasis. We include both anti- and pro-tumor immune effects, in addition to the experimentally observed phenomenon of tumor-induced immune cell phenotypic plasticity. Using geometric singular perturbation analysis, we derive a rather simple model that captures the main processes and, at the same time, can be fully analyzed. Literature-derived parameter estimates are obtained, and model robustness is demonstrated through a sensitivity analysis. We determine conditions under which the parameterized model can successfully explain both metastatic dormancy and blow-up. Numerical simulations suggest a novel measure to predict the occurrence of future metastatic blow-up, in addition to new potential avenues for treatment of clinically undetectable micrometastases.