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Chemotherapy as a cancer treatment can be traced back to
the ancient Egyptians, who used compounds of barley, pigs'
ears, and other ingredients to treat cancers of the stomach
and the uterus.
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During World War II, it was found that
soldiers who were exposed to sulfur mustard suffered
from lower white blood cell counts. This discovery led
to the use of nitrogen mustard, a similar but less toxic
chemical agent, to cure patients with high white blood
cells counts (lymphoid leukemia) and lymphomas. Later,
more chemical substances were studied and tested, becoming
chemotherapeutical drugs for cancer treatment.
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Chemotherapy is a distinctively different approach than surgery
and radiation therapy to treat cancer. Rather than physically
removing a tumor or a part of it, chemotherapy uses chemical
agents (anti-cancer or cytotoxic drugs) to interact with cancer
cells to eradicate or control the growth of cancer.
Cells divide by going through a cell
cycle ( Get 
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an ordered set of events that include the synthesis of DNA
(S-phase), mitosis
(M-phase), culminating in cell growth and division into two
daughter cells. Normal cells grow and die in a precisely controlled
way while cancer occurs when the process becomes abnormal,
with cells dividing and forming more cells without control
and order.
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In chemotherapy, drugs that interfere
primarily with DNA synthesis and mitosis (the S and
M phases of the cell cycle) are used to destroy cancer
cells. Different agents work through many different
mechanisms: some damage a cell's genetic material (DNA);
some prevent the cell from dividing.
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Since chemotherapeutic drugs cannot distinguish between normal
cells and cancer cells, both types of cells are affected by
chemotherapy. Toxicity of chemotherapeutic the agents to normal
cells is the cause of unpleasant side effects. However, the
value of chemotherapy lies in the fact that the killing effect
of chemotherapeutic agents has a definite selectivity for
cancer cells over normal host cells. Normal tissues are able
to repair themselves and continue to grow, so the injury caused
by chemotherapy is rarely permanent.
Chemotherapy as a cancer treatment option will be discussed
further in the next section.
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