Cancer Cells and Chemotherapy
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
More Chemotherapy Information:
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
Short & Long Term Side Effects of Chemotherapy
Cancer Clinical Trials