Cancer has become one of the leading causes of death and is on track to take the lead over heart disease. Animal studies continue to be at the forefront of cancer breakthroughs and achievements, saving hundreds of thousands of lives thanks to preclinical research. Though there has been progress over the past 20 years, researchers still find themselves challenged by the complex tumor microenvironment, tumor heterogeneity, and dynamic immune and metabolic responses. With less than 10% of cancer drugs receiving approval from the FDA, additional endpoints and biomarkers are needed to evaluate effectiveness and safety of treatments, and to also better understand the pathophysiology of tumors.