The reason is that there are over 200
different types of cells in the human body with each of these having
the potential to become cancerous. Cancer can develop in any of the
over 60 organs in the body. Cancers are named for the part of the
body where it started and the type of cell that has become
cancerous. All cancers start because abnormal cells grow out of
control. There are two general categories of cancer. Carcinomas are
cancers that develop on the surface linings of the organs. Sarcomas
are cancers that develop in the cells, and they affect solid
tissues, such as muscle and bone. They can also develop in the blood
vessels. Cancer tumors can either be malignant or benign.
Normal healthy cells divide and die as they should. The average
number of times normal healthy cells divide is known as the Hayflick
Limit. It was named after Dr. Leonard Hayflick, who in 1965 noticed
that cells divide a specific number of times before the division
stops. The average was between 40-60. (There is one woman who had
tissue in her body that could divide apparently forever: The Woman
with Immortal Cells)
If you took every cell in your body, at the time you were born, and
accounted for all the cells they would produce and multiplied that
number by the average time it takes for those cells to die, you get
what is known as the ultimate Hayflick limit or the maximum number
of years you can theoretically live. This is how researchers come up
with the theoretical life limit of 120 years.
For the first time since the government began collecting mortality
data early in the last century, cancer death rates began to decline
in 1993. It significantly declined from 1994 to 1998 with a
non-significant decline from 1998 to 2001 and falling death rates
from 2001 to 2008. In 2008, the death rate for all cancers was
175.67 per 100,000 people in the US. Cancer is not contagious.