The body is composed of many different types of cells that all grow, divide, and die in an orderly manner. This process is tightly regulated and controlled by the DNA machinery within cells.
While a person is growing up, the body cells divide rapidly to allow for development but once a person becomes an adult, most cells only divide to replace worn-out or dying cells or to repair injury.
When cells of the body at a particular site start to grow out of control, they may become cancerous. Cancer cell growth is different to normal cell growth. Instead of dying, cancer cells continue to grow and form new, abnormal cells. These abnormal cells are also capable of invading other tissues and can permeate the blood and lymphatic vessels which carry them to other sites in the body. This is called metastasis and is a property that normal cells do not possess.
Chemotherapy agents used in the treatment of cancer act by attacking rapidly dividing cells in the body, which includes the cancer cells. The various cytotoxic agents have different mechanisms of action for interrupting the cancer cell’s cycle so that mitosis or cell division is prevented. Some chemotherapy agents also act by inducing the cancer cells to undergo programmed cell death or apoptosis.
Cells that contain rapid growth factors such as those found in acute myelogenous leukemia and aggressive lymphomas are more sensitive to chemotherapy agents. In these cancers, a huge number of cells are constantly undergoing cell division and these form ideal targets for chemotherapy agents. Slow growing cancers on the other hand, are slow to respond to chemotherapy.