MT training: cancer medicine

Cancer chemotherapy is the treatment of cancer using drugs. It is the standard treatment for many types of cancer, and it produces cure of most patients who have choriocarcinoma, testicular cancer, adequate lymphocytic leukemia, or Hodgkin’s disease. Chemotherapy may be used alone or in combination with surgery and irradiation.

The field of pharmacokinetics (-kinetic means pertaining to movement) is concerned with the study of the distribution and disappearance of drugs in the body. Obviously the ideal is to develop drugs that ill large numbers of tumor cells without harming normal cells. Because some normal tissue cells such as bone marrow and gastrointestinal lining cells, have a rapidly dividing cell population, they suffer considerable damage from anti tumor drugs. Scientists working in various body fluids, such as blood plasma and urine, and use the information to design drug dosages and schedules of administration to achieve the greatest tumor kill with the least toxicity to normal cells.

Combination chemotherapy refers to the use of two or more anti tumor drugs together to kill a specific type of malignant growth. In chemotheraphy, drugs are given according to a written protocol, or plan, that details exactly how the drugs will be given. Usually drug therapy is continued until the patient achieves a complete remission, which is the absence of all signs of disease. At times, chemotherapy is given as an adjuvant (an aid) to surgery. This means that the drugs are used to kill possible hidden disease in patients who, after surgery, are otherwise free of any evidence of malignancy.

The following are categories of cancer chemotherapy therapeutic agents;

1. Alkylating agents—these are synthetic compounds two or more chemical groups called alkyl groups. The drugs interfere with the process of DNA synthesis by attaching to DNA molecules. Toxic side effects include nausea and vomiting, diarrhea, bone marrow depression (myelosuppression), and alopecia (hair loss). These are common side effects because the cells in the gastrointestinal tract, bone marrow, and scalp are rapidly dividing cells (high growth fraction) that, along with tumor cells, are susceptible to the lethal effects of chemotherapeutic drugs. The side effects disappear after treatment is suspended.

2. Antibiotics—these drugs are produced by bacteria or fungi. Many of these drugs act by binding to DNA and RNA in the cell, thus preventing normal replication. Toxic effects from their use include alopecia, stomatitis, myelosuppression, and gastrointestinal disturbances.

3. Antimetabolics—these drugs inhibit the synthesis of substances that are the necessary components of DNA or may directly block the replication or copying of DNA. Side effects are myelosuppression, with leucopoenia, thrombocytopenia, and bleeding; and oral and digestive tract toxicity, including stomatitis (sore mouth), nausea and vomiting.

4. Plant derivatives—these drugs are chemicals derived from plants. They are used frequently in combination with other chemotherapeutic agents. Side effects include myelosuppression, alopecia, and nerve damage.

5. Steroids—these are a class of chemicals made by glands in the body, and they have important effects on reproduction, energy production, and aging. Examples are estrogens and androgens. These hormones exert their action by attaching to receptor proteins in target tissues. The growth of some tumors (breast and prostate) is often dependent on steroid hormones. Some breast cancers have estrogen receptors (ER) and will respond to the removal of estrogen by oophorectomy or the use of antiestrogen drugs, such as tamoxifen, that block estrogenic effects. Fluid retention, masculinization or feminization, nausea, and vomiting are some possible side effects of various steroids.

Biological Therapy

A more recent approach to cancer treatment is the use of the body’s own defense mechanisms to fight tumor cells. Investigators explore how the elements of the immune system can be restored, enhanced, mimicked, and manipulated to destroy cancerous cell. Substances produced by normal cells that either directly block tumor growth or stimulate the immune system and other body defenses are called biological response modifiers. Examples of these substances are interferon (made by lymphocytes), monoclonal antibodies (made by mouse cells and capable of binding to human tumors), colony-stimulating factors (CSFs) that stimulate blood-forming cells and reverse the effects of chemotherapy, and interleukins that stimulate the immune system to destroy tumors.