There is a large body of evidence proving that all the cells within a tumor mass are derived from a single cell. Imagine; one damaged cell can lead to a life-threatening tumor. The magnitude of the true meaning behind this is difficult to grasp because it is an extremely shocking and frightening revelation.

Even though all the cells within a tumor mass may be derived from a single cell, this does not mean that all the cells in a tumor are genetically identical like you might expect. Tumor cells are more unstable than normal cells, meaning they mutate at a much higher rate and they repair themselves much less effectively. Therefore, the cells within a tumor are different even from one another.

Fortunately, the chain of events leading to a single cell becoming a cancerous tumor consisting of millions of its offspring is a rare event. Actually, it is not just a single event that causes this, but several events that must occur in a specific sequence.

First, a piece of the DNA strand must be significantly mutated (we will talk about how this might happen later) and the mutations must slip through the repair mechanisms. These mutations may take place over generations of cells. For example, one generation may have one mutation; the next may not have any. A subsequent generation may have another and so on, until the "cancer mutations" have occurred.

Due to these mutations, the cell must gain the ability to proliferate (divide rapidly) and thus lose its normal function. In a sense, the major purpose of the cell must be to divide.

There are probably only a limited number of alterations that will allow a cell to lose its functions and divide out of control. Some alterations affect nothing, others may cause a minor change that is not really threatening to the cell, and still others can outright kill the cell. So, to become cancerous, the cell must maintain its ability to divide without causing any damage to limit its ability to survive.

If a cell becomes bent on dividing, the cell will just continue dividing and crowd out other cells within the area. In some fortunate cases an individual's own immune system may actually stop the growth of the tumor. The immune system may recognize that the cells within the tumor are not normal. If this happens, the immune cells will then have an easy time destroying the tumor. This may take place a number of times throughout an individual's life without them ever being affected.

If a tumor goes unnoticed and begins to grow, a lack of nutrients can eventually limit its growth. If nutrients are not continuously supplied, the tumor cells cannot metabolize. In this case, at the very least, no new growth can occur. If a tumor becomes unable to grow and unable to support some of its functions and cell death occurs, the tumor may go into a dormant state. In this case it cannot spread. This is called carcinoma "in situ", which means "in place". Once the tumor reaches this limiting size, (which is no bigger than a pea), and if it is unable to get more nutrients, it will stay in this dormant state and may eventually die off.

Autopsies have shown that 40% of women in their 40's have these tiny "in situ" tumors (not capable of spreading) in their breasts. Had some of these females lived longer, they might have developed breast cancer when they were older. However, many of these women would never develop cancer.

The tiny tumors would not have been able to get the necessary nutrients to grow any larger. A tumor in this situation cannot do any damage. It will usually just die off. An individual could actually have several of these stationary, "in situ" tumors and still live to a healthy, old age, completely unaffected by the tumors. Researchers are trying to develop tests that will determine whether an individual's breast and prostate tumors will remain dormant or spread. In that way, patients in the future could be spared unnecessary treatments.