1.1 Definition of Cancer
Cancer is a term used for diseases in which abnormal cells
divide without control and are able to invade other tissues.
Cancer cells can spread to other parts of the body through
the blood and lymph systems. Cancer is not just one disease
but many diseases. There are more than 100 different types
of cancer. Most cancers are named for the organ or type of
cell in which they start. Cancer types can be grouped into
broader categories. The main categories of cancer include:
1. Carcinoma - cancer that origins in the skin or in tissues
that line or cover internal organs.
2. Sarcoma - cancer that begins in bone, cartilage, fat,
muscle, blood vessels, or other connective or supportive
tissue.
3. Leukemia - cancer that starts in blood-forming tissue
such as the bone marrow and causes large numbers of
abnormal blood cells to be produced and enter the blood.
4. Lymphoma and myeloma - cancers that begin in the
cells of the immune system.
5. Central nervous system cancers - cancers that begin in
the tissues of the brain and spinal cord.
1.2 How Cancer Starts
All cancers begin in cells, the body's basic unit of life. To
understand cancer, it's helpful to know what happens when
normal cells become cancer cells. The body is made up of
many types of cells. These cells grow and divide in a
controlled way to produce more cells as they are needed to
keep the body healthy. When cells become old or damaged,
they die and are replaced with new cells. However,
sometimes this orderly process goes wrong. The genetic
material (DNA) of a cell can become damaged or changed,
producing mutations that affect normal cell growth and
division. When this happens, cells do not die when they
should and new cells form when the body does not need
them. The extra cells may form a mass of tissue called a
tumor. The effect on DNA is called nano effect.
Fig 1: spreading of metastatic cancer cells invade lymph vessels
and blood vessels
1.3. Site of Cancer Development in Human body:
The most common sites of cancer metastasis are the lungs,
bones, and liver. Although most cancers have the ability to
spread to many different parts of the body, they usually
spread to one site more often than others. The following
table shows, in descending order from left to right, the three
most common sites of metastasis, excluding lymph nodes,
for several types of cancer: