Every day within our bodies, a massive process of destruction and repair occurs. The human body is comprised of about 15 trillion cells, and every day billions of cells wear out or are destroyed. In most cases, each time a cell is destroyed the body makes a new cell to replace it, trying to make a cell that is a perfect copy of the cell that was destroyed because the replacement cell must be capable of performing the same function as the destroyed cell. During the complex process of replacing cells, many errors occur. Despite remarkably elegant systems in place to prevent errors, the body still makes tens of thousands of mistakes daily while replacing cells either because of random errors or because there are outside pressures placed on the replacement process that promote errors. Most of these mistakes are corrected by additional elegant systems or the mistake leads to the death of the newly made cell, and another normal new cell is produced. Sometimes a mistake is made, however, and is not corrected. Many of the uncorrected mistakes have little effect on health, but if the mistake allows the newly made cell to divide independent of the checks and balances that control normal cell growth, that cell can begin to multiply in an uncontrolled manner. When this happens, a tumor (essentially a mass of abnormal cells) can develop colon cancer.
Tumors fall into two categories: there are benign (noncancerous) tumors and malignant (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 sometimes can grow quite large or rapidly and cause severe symptoms, even death, although most do not. For example, a fibroid tumor in a woman’s uterus is a type of benign tumor. It 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 lymphatic system, so they are unable to travel to other places in the body and grow. A cancer, on the other hand, can shed cells that can travel through the blood or lymphatic system, landing in tissues distant from the primary tumor and growing into new tumors in these distant tissues. This process of spreading to distant tissues, called metastasis, is the defining characteristic of a cancerous or malignant tumor.