How Cells Turn Into Cancer Cells - Chapter 1 Introduction To Preventing Cancer: Cancer

Content provided by the Faculty of the Harvard Medical School

How cells turn into cancer cells

The first step in this long process is known as initiation, which occurs when DNA, the genetic material contained within a normal cell, suffers some type of permanent change or mutation. Once the gene has mutated, the instructions it provides to the cell also change. Genetic mutation is responsible for initiating the series of events that - unimpeded - can lead to cancer.

Genetic mutations can occur in a number of ways. You may inherit a damaged gene, for example, or a gene may inadvertently mutate or change during normal cell replication. It's often a matter of chance: every million divisions or so, a mistake happens. More often, genes mutate because they are exposed to some type of initiator, a broad category of substances that includes well-known carcinogens such as the ultra-violet radiation in sunlight and the toxins in tobacco smoke, as well as some substances most people have never heard of. Although the mechanisms of damage vary, all initiators inflict some permanent change in a cell's DNA. For example, oxygen free radicals are highly reactive molecules that are first produced as byproducts of normal cellular activity. What makes these initiators so volatile and potentially damaging to cells is that they have an unpaired electron. This makes them unstable, and they try to fill that empty electron slot by raiding healthy cells for additional electrons. The cell under siege by a free radical becomes unstable itself, and as a result may begin to function erratically, by doing such things as duplicating damaged DNA. Viruses such as the human papillomavirus and bacteria such as Helicobacter pylori can also function as initiators.

Genetic mutations are unpredictable and change different aspects of how a cell functions. The mutation becomes significant when it affects one of the genes that govern cell growth and replication. Normally, cells have several of these genes, known as proto-oncogenes. An initiator can turn such genes into oncogenes, which then make the cells more likely to develop into cancer.

Other substances known as promoters, such as alcohol or certain hormones, encourage cells to replicate faster than they normally would. Promoters are a bit like fertilizers: they encourage things to grow. When a cell is already inclined to be cancerous, because it has been initiated in some way, promoters push it further in that direction.

How a Cell Mutates DNA, the genetic material in the cell nucleus, can be damaged by highly reactive oxygen molecules known as free radicals or by an initiator such as tobacco smoke. Once the DNA is damaged, in a process called mutation, the cell reproduces itself and may be encouraged to multiply rapidly by promoters such as hormones. It is this rapid, out-of-control cell growth that produces a malignant tumor.

Last updated:	May 01, 2008