In this scenario, a tumor cell in the colon has multiplied into a small, harmless mass in the epithelium, which is a layer of cells that line all of the body's organs. At this point, the tumor cells (shown with red nuclei) are beginning to crowd out the surrounding "normal" cells. Most healthy people actually have small tumors like these that never grow to be harmful.
In a process called metastasis, tumor cells migrate to other locations in the body (like the liver) and, through cell division, establish colonies. In this example of late-stage cancer, healthy cells (upper left) are crowded out by the growing number of cancer cells being fed by red blood vessels.
To view Children's new interactive presentation that illustrates what happens between the appearance of the first cancer cell and complete organ failure, go to www.childrenshospital.org/research/cancer.