The area of cancer research has become a very actively researched field. The different transitions from cell division to apoptosis are recently under extensive investigations. Apoptosis is a generally controlled mechanism of cell death that is essential for the elimination of cells that can no longer replicate or that have potentially mutagenic damage during normal development and for the maintenance of tissue homeostasis. Research in and around apoptosis has increased substantially since the early 1990s. In addition to its importance as a biological phenomenon, defective apoptotic processes have been implicated in an extensive variety of diseases. Development of drug resistance in tumor cells is common occurrence, and is the primary reason for failure of chemotherapy. A number of biochemical changes could contribute to the development of cellular resistance to chemotherapy. The book is the outgrowth of Ph.D. dissertation that shed the light on new mechanisms that might contribute to cancer development and/or progression and elucidate molecular based-variation that is important from both basic and clinical perspectives.