Pancreatic Cancer (cont.)

Every second of every day within our body, a massive process of destruction and repair occurs. The human body is comprised of trillions of cells, and every day billions of cells wear out or are destroyed. Each time the body makes a new cell to replace one that is wearing out, the body tries to make a perfect copy of the cell that dies off, because that dying cell had a job to do and the newly made cell must be capable of performing that same function. Despite remarkably elegant systems in place to edit out errors in this process, the body makes tens of thousands of mistakes daily in normal cell division either due to random errors or from environmental pressure within the body. Most of these mistakes are corrected, or the mistake leads to the death of the newly made cell and another new cell is then made. Sometimes a mistake is made that, rather than inhibiting the cell's ability to grow and survive, allows the newly made cell to grow in an unregulated manner. When this occurs, that cell can begin to divide independent of the checks and balances that control normal cell growth. When this happens a tumor can develop.

Tumors fall into two categories; there are "benign" tumors and "malignant" or cancerous tumors. So what is the difference? The answer is that a benign tumor grows only in the tissue from which it arises. Benign tumors can sometimes grow quite large or grow rapidly and cause severe symptoms. For example, a fibroid in a woman's uterus can cause bleeding or pain, but it will never travel outside the uterus and grow as a new tumor elsewhere. Fibroids, like all benign tumors, lack the capacity to shed cells into the blood and lymph systems and cannot travel to other places in the body and grow. A cancer, on the other hand, can shed cells from the primary tumor that can float like dandelion seeds in the wind through the bloodstream or lymphatics, landing in tissues distant from the primary tumor, growing new tumors in various other sites. This process, called metastasis, is the defining characteristic of a cancerous tumor. Pancreas cancer, unfortunately, is a particularly good model for this process.

Cancers are named by the tissues from which the primary tumor arises. Hence, a lung cancer that travels to the liver is not a "liver cancer" but is described as metastatic lung cancer and a patient with a breast cancer which spreads to the brain is not described as having a "brain tumor" but rather as having metastatic breast cancer.

Source: MedicineNet.com
http://www.medicinenet.com/pancreatic_cancer/article.htm