The goals of chemotherapy (and radiotherapy) are to eliminate tumor cell targets by promoting cell death. In recent years, a major focus has been placed on programmed cell death or apoptosis as the primary mechanism of cell killing. However, tumor cells may respond to various forms of treatment in diverse ways, only some of which culminate in cell death and loss of clonogenic survival. In addition to apoptosis, cell death may occur through mitotic catastrophe, autophagy (a subtype of apoptosis), or anoikis. Alternatively, cells may undergo either transient or prolonged growth arrest; in addition, senescence arrest or accelerated senescence is now recognized as a response to various treatments,.
