What Is Cancer: Preventing And Treating Colorectal Cancer

Content provided by the Faculty of the Harvard Medical School

What is cancer?

Cancer is not a single disease; rather, it is a group of diseases characterized by the presence of cells that grow out of control. Most types of cancer form a tumor, a lump or mass of cancerous cells. Cells from a tumor may break away and travel to other parts of the body, where they can settle and multiply — a process called metastasis. Not all tumors are cancerous (malignant). Some are benign (nonmalignant), don't spread, and aren't life-threatening. A few cancers don't form tumors at all — for example, those that affect the blood, such as leukemia.

The cells of the body continually reproduce themselves. As new cells arise, older ones die out. In this way, your body remains healthy. Orchestrating this process are the genes contained in the nucleus of every cell. These genes consist of strands of DNA (deoxyribonucleic acid), which function like detailed molecular blueprints, providing instructions on everything from your hair color to your metabolism. They also produce proteins that provide the stop and go signals for the processes of growth and development. The process of orderly and planned cell death is called apoptosis. When it works well, apoptosis helps your body maintain a delicate balance between old cells and new ones.

Cancer is a perversion of this normal process. What was once orderly becomes chaotic and unmanageable. Normal cells contain built-in "stop" signals that tell them when to stop dividing; cancer cells have lost these signals and continue to multiply. Normal cells replicate at a steady pace; cancer cells replicate much more rapidly. Normal cells maintain a balance between old and new; cancer cells never die, building up in such numbers that a tumor forms. Normal cells respect boundaries and stay put; cancer cells migrate or metastasize elsewhere.

The problem begins when DNA, the genetic material contained within a normal cell, suffers some type of permanent change, or mutation. Genetic mutations are responsible for initiating the series of events that, unimpeded, can lead to cancer.

Last updated:	April 09, 2009