Spread of tumors to distant locations is of great importance in cancer
About ninety percent of the deaths due to cancer
involve tumors that have spread around the body. The movement of tumor cells to
other parts of the body
is known as metastasis. Metastasis is a complex process
During which cancer cells break off the original
or primary tumor and move through the body to form tumors at new locations
From the point of view of a cancer cell, this is a dangerous
and often unsuccessful process A trip through the body is full of hazards that
cause the death of most cells that begin the journey
even tough cancer cells. To begin the process
individual cells must break away from the tumor and invade nearby vessels
The cells crawl along the surface of other cells
and the fibrous stringy structures surrounding them
and then force their way in. Shown here
is the invasion of the blood supply. Once inside a blood vessel,
the cancer cells may parish from a variety of causes
Some cells die simply because they are unable to survive
floating around in the bloodstream.
Others may become damaged and die when they squeeze through tight spaces
or bump into the walls of the blood
vessels.
Still other migrating cells may be recognized and destroyed
by cells of the immune system.
How and where the migrating cells stop is different for different cancer types
Once the tumor cells are no longer moving
they can begin the process of forming a new tumor
by leaving the blood vessel and beginning to reproduce in the new
location
This does not always occur and cells that have made it this far may still die
or fail to divide If the new environment
is suitable the newly-arrived cell will begin to grow
and a new tumor will develop.