Chemotherapy, as it refers to cancer treatment, is a generic term and includes many different drugs with a wide variety and severity of side effects. Generalizations regarding specific side effects and toxicities are difficult to make.

Cancer chemotherapy kills or arrests the growth of cancer cells by targeting specific parts of the cell growth cycle. However, normal healthy cells share some of these pathways and thus are also injured or killed by chemotherapy. This is what causes most side effects from chemotherapy.

Chemotherapy usually targets rapidly dividing cells. Some normal cells -- including blood cells, hair, and cells lining the gastrointestinal tract -- are also rapidly dividing and thus these are the normal cells most likely to be damaged.

Newer cancer therapies, some of which have already been approved by the FDA, are more specifically targeted at growth pathways that are only found in cancer cells. These drugs may be more effective while also being less toxic.

Types of chemotherapy drugs

Chemotherapy drugs are classified based on how they work. The main types of chemotherapy drugs are described below:

• Alkylating drugs kill cancer cells by directly attacking DNA, the genetic material of the genes. Cyclophosphamide is an alkylating drug.
• Antimetabolites interfere with the production of DNA and keep cells from growing and multiplying. An example of an antimetabolite is 5-fluorouracil (5-FU).
• Antitumor antibiotics are made from natural substances such as fungi in the soil. They interfere with important cell functions, including production of DNA and cell proteins. Doxorubicin and bleomycin belong to this group of chemotherapy drugs.
• Plant alkaloids prevent cells from dividing normally. Vinblastine and vincristine are plant alkaloids obtained from the periwinkle plant.
• Steroid hormones slow the growth of some cancers that depend on hormones. For example, tamoxifen is used to treat breast cancers that depend on the hormone estrogen for growth.