Chemotherapy

Chemotherapy is the use of cytotoxic agents to destroy cancer cells. Chemotherapy dates back to the 1500s, when heavy metals were used systemically to treat cancers, and severe toxicity and limited cure were reported. Since then, a vast spectrum of antineoplastic drugs has been discovered to achieve cure, control, and palliation of many cancers. The new and improved changes in the drug approval process of the Food and Drug Administration have speeded the entry of novel drugs that have made chemotherapy a vital part of the cancer armamentarium. Chemotherapy remains the primary treatment for some malignancies and an adjunct to other treatment modalities (surgery, radiation, and immunotherapy). Unlike surgery and radiation, chemotherapy is distinguished by its systemic effects. Most of the drugs are transported by the bloodstream; most do not cross the blood–brain barrier and therefore cannot reach the central nervous system.

To achieve the above goals, chemotherapeutic drugs (as single agents or in combination) may be used in the following strategies:
Adjuvant: A short course of high-dose, usually combination drugs is given after radiation or surgery to destroy residual tumor cells.
Consolidation: Chemotherapy is given after induction therapy has achieved a complete remission; the regimen is repeated to increase the cure rate or to prolong patient survival.

Induction: This term is commonly used in the treatment of hematologic malignancies. It refers to the use of usuallya combination of high-dose drugs to induce a complete response when initiating a curative regimen.
Intensification: After complete remission is achieved, the same agents used for induction are given at higher doses, or different agents are given at high doses to effect a better cure rate or a longer remission.
Maintenance: Single or combination, low-dose cytotoxic drugs are used on a long-term basis in patients who are in complete remission to delay regrowth of residual cancer cells.

Neoadjuvant: Adjuvant chemotherapeutic drugs are used during the pre- or perioperative period.
Palliative: Chemotherapy is given to control symptoms, provide comfort, and improve quality of life if cure is impossible.
Salvage: A potentially curative high-dose regimen is given to a patient whose symptoms have recurred or whose treatment has failed with another regimen.
The human body is composed of an intricate network of nondividing and dividing cells organized into various tissues that perform specific functions. Nondividing cells, such as striated muscle cells and neurons, are highly differentiated and do not need to replicate to maintain their function. Dividing cells, such as germ, epithelial, and bone marrow stem cells, must replicate to maintain their function.

The body regulates all replication of dividing cells by maintaining a balance between the birth and death of cells. The body's maintenance of this homeostasis depends on the synthesis of trigger proteins, or signals, in response to cell death. This synthesis stimulates the entry and movement of dividing cells through the process of cell division.