The tumor micro-environment, including the intratumoral mechanical forces, the tumor vasculature and the immune micro-environment, play a crucial role in tumor progression and cancer treatment. However, owing to the complexity of the cancer system, its multiscale nature and spatiotemporal dynamics, the integration of the knowledge of the interactions among the various tumor components in order to understand the system response to therapeutics and make reliable predictions for optimal treatment is challenging. The application of principles of engineering and physical sciences to oncology has provided powerful insights into the mechanisms by which these factors affect tumor progression and confer resistance to delivery and efficacy of molecular, nano-, and immuno-medicines. In my talk, I will present a mathematical framework that relates cellular and sub-cellular events to macroscopic tumor growth and treatment response that my group developed in collaboration with the teams of Dr. Rakesh K. Jain and Dr. Lance L. Munn (Massachusetts General Hospital/Harvard Medical School). Apart from the proliferation and migration of cancer cells, our model also accounts for i) biological and mechanical interactions of the tumor with the host tissue, ii) the tumor-induced angiogenesis and its modulation by growth factors and pro-inflammatory cytokines, iii) the immune system, incorporating both innate and adaptive immune cells, such as tumor-associated macrophages, natural killer cells, CD4+/CD8+ T cells as well as regulatory T cells, and iv) the systemic delivery of therapeutics. I will further discuss applications of the model for the derivation of guidelines for optimal use of strategies that we developed to reengineer the tumor micro-environment by normalizing the tumor vasculature and the extracellular matrix in order to improve cancer immunotherapy. Finally, I will present recent developments for the extension of the model to incorporate SARS-CoV-2 virus infection and the progression of the COVID-19 disease.