Introduction to Chemotherapy
During World War II, it was found that soldiers who were exposed to sulfur mustard suffered from lower white blood cell counts. This discovery led to the use of nitrogen mustard, a similar but less toxic chemical agent, to cure patients with high white blood cells counts (lymphoid leukemia) and lymphomas. Later, more chemical substances were studied and tested, becoming chemotherapeutical drugs for cancer treatment.
Chemotherapy is a distinctively different approach than surgery and radiation therapy to treat cancer. Rather than physically removing a tumor or a part of it, chemotherapy uses chemical agents (anti-cancer or cytotoxic drugs) to interact with cancer cells to eradicate or control the growth of cancer.
Cells divide by going through a cell cycle, following an ordered set of events that include the synthesis of DNA (S-phase), mitosis (M-phase), culminating in cell growth and division into two daughter cells. Normal cells grow and die in a precisely controlled way while cancer occurs when the process becomes abnormal, with cells dividing and forming more cells without control and order.In chemotherapy, drugs that interfere primarily with DNA synthesis and mitosis (the S and M phases of the cell cycle) are used to destroy cancer cells. Different agents work through many different mechanisms: some damage a cell's genetic material (DNA); some prevent the cell from dividing.
Since chemotherapeutic drugs cannot distinguish between normal cells and cancer cells, both types of cells are affected by chemotherapy. Toxicity of chemotherapeutic agents to normal cells is the cause of unpleasant side effects. However, the value of chemotherapy lies in the fact that the killing effect of chemotherapeutic agents has a definite selectivity for cancer cells over normal host cells. Normal tissues are able to repair themselves and continue to grow, so the injury caused by chemotherapy is rarely permanent.