How Cancer Starts, How Cancer Spreads, Where and Why

The number of cells in a tissue is determined by the balance between cell division and cell
death. Uncontrollable cell division leads to formation of abnormal growths called tumors.
Tumors can be benign or malignant. Benign tumors are slow growing and constrained by surrounding
connective tissue so they do not spread to other organs. They can still be harmful or even kill by
pressing on nearby nerves, blood vessels, or brain tissue. Examples of benign tumors include
pituitary tumors which may press on optic nerves and cause loss of vision. Cancers are malignant
tumors. Tumors that can spread beyond the limit of the original organ where it comes from and to
other organs of the body. Cancer starts from damage in the DNA of a cell. This DNA damage is
called mutation. Mutations happen when the cell duplicates its DNA prior to cell division and
makes mistakes. These damages are usually detected and repaired before the cell can divide but
sometimes some of them may be ignored and transferred to daughter cells. If the mutation is located in
one of many genes that control the cell cycle, it may affect the regulation of cell cycle in the
cell carrying it and make the cell divide faster than it’s supposed to. Usually, one mutation is
not enough to cause cancer but as it makes the cell cycle control less reliable, many more DNA
damages or mutations would go unnoticed. Cancer is usually the result of accumulation of many
mutations of genes involved in cell cycle control and DNA repair. This commonly happens over a long
period of time over many rounds of cell divisions and this explains why cancers are more common in
older people. Some people are said to be predisposed to cancer. This is because they
are born with a mutation that makes them more likely to develop a certain type of cancer. This
mutation alone is not enough to cause cancer but it starts the process of making the cells cancerous.
The person carrying it is one step further down the road towards developing a cancer than others
who do not have the mutation. Cancer cells do not stick together like normal cells. They move and
invade nearby tissues and organs. This is local spread. They may also spread to further away
organs by means of blood or lymph circulation. This is systemic spread. Metastasis is the spreading of
cancers to non-adjacent organs. Cancer cells from the original tumor or primary cancer can break
out and may be taken up by a blood or lymph vessel for a ride throughout the body. They can then
squeeze out from the vessel into other tissues and start a new tumor growth in the new location
which will become secondary cancer. While traveling in the bloodstream, a cancer cell usually stops at
the first place where the vessel is getting so narrow that it gets stuck. As blood flow from
most organs goes to the capillaries of the lungs, this is where cancer is spread the most. Lungs are
indeed the most common site of secondary cancers. Likewise, while traveling in the lymphatic system,
cancer cells commonly get stuck in the nearest lymph nodes where the vessels get narrower. This
is the reason why surgeons usually remove nearby lymph nodes when removing tumors.

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