Metastasis: The Big Problem

Metastasis: The Big Problem
by L A Parmley

All tissues have linings around them to keep the different cell types (those of the tissue and those outside the tissue) separate. In instances where angiogenesis has occured, the tumor cells may break through these linings which act as boundaries limiting normal growth. This is termed tumor invasion.

An invasive tumor breaks through the membrane, or the lining of the tissue. Several events must occur in order for a tumor to become invasive. First, a tumor cell must actually break away from the rest of the tissue mass. It will then need to move toward the lining of the tissue. The cell moves by extending little blebs or "fingers" that allow it to crawl along in a specific direction - similar to the way a snail moves.

Once at the membrane, the tumor cell will have to release several particular enzymes, all acting to dissolve the membrane lining away. If this can be achieved, the tumor cell will move into the new space on the other side of the membrane. It will have broken the normal limits of cell growth in the tissue.

The invasion by the tumor will allow it to spread to another tissue type or possibly a capillary. Capillaries may lead to a blood vessel, which would grant the tumor cell access to the blood stream. If this happens, metastasis, or tumor spreading may occur.

Metastasis is the most serious stage of cancer. Tumor metastasis occurs when a few tumor cells have separated from the tumor mass and have "seeded" themselves at one or more new regions in the body. Once in this new area, they will multiply and eventually crowd out the normal cells. At some point, nearby tissues and organs may become so crowded they will not be capable of performing the functions necessary to maintain life.

Metastasis occurs when tumor cells move away and seed themselves in tissues that are distant from the original tumor. Most often, the tumor metastasizes to the lymph nodes nearest the tumor. The tumor cells travel to a new area by moving through the blood stream or the lymph stream of the immune system. The cells move through the blood or lymph stream until they reach a capillary wall. They make their way through it by dissolving the wall (or membrane) and moving through the space into the new tissue. In this manner, the tumor will "seed" itself to a new area.

Fortunately, the few tumor cells that do make their way into the bloodstream do not survive for very long in the blood. Less than 0.1% actually survive the journey to metastasize.

Oddly enough, most cases of metastasis are to only a few different tissues. Usually, the metastasis occurs to a patient's lung or their lymph nodes. Researchers believe that certain chemicals may be released by these organs that somehow attract tumor cells. This is a currently an important area of study because many more patients could be treated successfully if metastasis could be stopped.

It has been estimated that about 50% of all cancer patients may have metastasis by the time they are finally diagnosed and treated. The chances of successfully treating metastatic disease with current therapies is less than the chance of successfully treating pre-metastatic disease. However, there are many instances where patients with even extremely severe cases of metastatic cancer are cured. With the numerous new discoveries, the chances of curing metastatic disease will only climb in the future.