The bi-directional interactions between the tumor and the tumor microenvironment. Tumor-microenvironment interactions are bidirectional. Each of the interaction partners is capable of regulating gene expression in the other partner, or of exerting selective pressures on it. Each interaction partner thus shapes the phenotype of the other partner. Interactions of cancer cells with components of their microenvironment are crucial determinants in the decision making process determining if cancer cells will progress towards metastasis, if they will stay dormant or if they will disappear altogether.