Cancer is a complicated and multifaceted disease that is caused by changes in genes and epigenetics. These problems are what cause cells to multiply and stay alive without control. This chapter gives a complete overview of cancer biology by focusing on the most important molecular and cellular processes that cause tumors to grow from the inside out. Among the key characteristics of cancer that we investigate are persistent proliferative signals, evasion of growth suppressors, resistance to cell death, the capacity to create replicative immortality, the activation of invasion and metastases, and the generation of angiogenesis. All of these traits are necessary for the development of cancer. Additionally, discuss new markers and enabling traits, including genomic instability, inflammation, unregulated cellular energetics, and immunological evasion. Understanding these markers helps explain cancer and design targeted medicines. It discusses how cancer cells and their microenvironment interact and how the tumor microenvironment affects cancer growth and medication resistance. This chapter closes the distance between basic cancer research and clinical practice by including molecular biology, genetics, and clinical oncology. This is crucial to develop cancer treatment from radiology to radiation oncology, which demands a strategy involving several disciplines using radiology as the basis.