Doctors and scientists can't say for sure what causes each case of oral cavity or oropharyngeal cancer. But they do know many of the risk factors and how some of them cause cells to become cancerous.

Cancers develop when the DNA of cells are damaged. DNA contains genes -- the instructions for how the cells in our bodies function. Some of these genes help cells grow at a proper rate. If these genes are altered, the cells may grow out of control and form a tumor.

Tobacco and alcohol can damage cells in the lining of the oral cavity and oropharynx. The cells in this layer must grow more rapidly to repair this damage. The more often cells need to divide, the more chances there are for them to make mistakes when copying their DNA which may increase their chances of becoming cancerous.

Many of the chemicals found in tobacco can damage DNA directly. Scientists are not sure whether alcohol directly damages DNA, but they have shown that alcohol helps many DNA-damaging chemicals get into cells more easily. This may be why the combination of tobacco and alcohol damages DNA far more than tobacco alone.

This damage can cause certain genes (for example, those in charge of starting or stopping cell growth) to malfunction. Abnormal cells can begin to build up, forming a tumor. With additional damage, the cells may begin to spread into nearby tissue and to distant organs.

In cases where human papilloma virus (HPV) infection may be involved, scientists think the virus causes cells to make 2 proteins known as E6 and E7. When these are made, they turn off some genes responsible for keeping cell growth in check. Uncontrolled cell growth may in some cases lead to cancer.

Last Medical Review: 09/24/2009
Last Revised: 09/24/2009