Clinical meaning
Chemotherapy is the systemic administration of cytotoxic drugs designed to destroy cancer cells or inhibit their growth and division. The fundamental principle underlying chemotherapy is that cancer cells divide more rapidly and less controllably than most normal cells, making them more susceptible to drugs that interfere with cell division. However, because chemotherapy targets the mechanisms of cell division rather than cancer-specific markers, it also damages normal rapidly dividing cells -- particularly bone marrow stem cells, gastrointestinal epithelial cells, and hair follicle cells -- producing the characteristic side effects of myelosuppression, mucositis, and alopecia. The cell cycle is the ordered sequence of events by which a cell duplicates its contents and divides into two daughter cells. It consists of four distinct phases: G1 (Gap 1, the cell grows and prepares for DNA synthesis), S phase (Synthesis, where DNA is replicated), G2 (Gap 2, the cell prepares for mitosis by synthesizing proteins needed for cell division), and M phase (Mitosis, where the cell physically divides into two daughter cells). Cells that are not actively dividing enter a resting state called G0. Chemotherapy...