Cancerous tumors are characterized by cell division, which is no longer controlled as it is in normal tissue. "Normal" cells stop dividing when they come into contact with like cells, a mechanism known as contact inhibition. Cancerous cells lose this ability. Pictures of cancer cells show that cancerous cells lose the ability to stop dividing when they contact similar cells.
Cancer cells no longer have the normal checks and balances in place that control and limit cell division. The process of cell division, whether normal or cancerous cells, is through the cell cycle. The cell cycle goes from the resting phase, through active growing phases, and then to mitosis (division).
The ability of chemotherapy to kill cancer cells depends on its ability to halt cell division. Usually, cancer drugs work by damaging the RNA or DNA that tells the cell how to copy itself in division. If the cancer cells are unable to divide, they die. The faster that cancer cells divide, the more likely it is that chemotherapy will kill the cells, causing the tumor to shrink. They also induce cell suicide (self-death or apoptosis).
Chemotherapy drugs that kill cancer cells only when they are dividing are called cell-cycle specific. Chemotherapy drugs that kill cancer cells when they are at rest are called cell-cycle non-specific. The scheduling of chemotherapy is set based on the type of cells, rate at which they divide, and the time at which a given drug is likely to be effective. This is why chemotherapy is typically given in cycles.
Chemotherapy is most effective at killing cells that are rapidly dividing. Unfortunately, chemotherapy does not know the difference between cancer cells and the normal cells. The "normal" cells will grow back and be healthy but in the meantime, side effects occur. The "normal" cells most commonly affected by chemotherapy are the blood cells, the cells in the mouth, stomach and bowel, and the hair follicles; resulting in low blood counts, mouth sores, nausea, diarrhea, and/or hair loss. Different drugs may affect different parts of the body.
Chemotherapy (anti-neoplastic drugs) is divided into five classes based on how they work to kill cancer. Although these drugs are divided into groups, there is some overlap among some of the specific drugs. Further sections discuss several different types of chemotherapy in the effort to further explain these important procedures.
More Chemotherapy Information:
Chemotherapy Terms Chemotherapy Protocols - How Chemotherapy Works How Chemotherapy Is Given How Doctors Decide Which Chemotherapy Drugs To Give How Long Chemotherapy Is Given How To Tell If Chemotherapy Is Working Cancer Cells & Chemotherapy Types of Chemotherapy Targeted Therapy The Immune System About Immunotherapy Hormone Therapy Chemoporotective Agents Chemotherapy Resistance Short & Long Term Side Effects of Chemotherapy Nadir Cancer Clinical Trials