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 (see “What are the risk factors for oral cavity and oropharyngeal cancers?”) and how some of them may lead to cells becoming cancerous.
Scientists believe that some risk factors, such as tobacco or heavy alcohol use, may cause these cancers by damaging the DNA of cells that line the inside of the mouth and throat.
DNA is the chemical in each of our cells that makes up our genes — the instructions for how our cells function. We usually look like our parents because they are the source of our DNA. However, DNA affects more than how we look. Some genes called proto-oncogenes can help control when cells grow and divide. DNA changes can change these into genes that promote cell division that are called oncogenes. Some genes that slow down cell division or make cells die at the right time and are called tumor suppressor genes. DNA changes can turn off tumor suppressor genes, and lead to cells growing out of control. Cancers can be caused by DNA changes that create oncogenes or turn off tumor suppressor genes.
When tobacco and alcohol damage the cells lining the mouth and throat, 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 human papilloma virus (HPV) infections, the virus causes cells to make 2 proteins known as E6 and E7. When these are made, they turn off some genes that normally help keep cell growth in check. Uncontrolled cell growth may in some cases lead to cancer. When HPV DNA is found in the tumor cells, especially in non-smokers who drink little or no alcohol, HPV is thought to be the likely cause of the cancer.
Some people inherit DNA mutations (changes) from their parents that increase their risk for developing certain cancers. But inherited oncogene or tumor suppressor gene mutations are not believed to cause very many cancers of the oral cavity or oropharynx.
Some oral cavity and oropharyngeal cancers have no clear cause. Some of these cancers may be linked to other, as of yet unknown risk factors. Others may have no external cause — they may just occur because of random DNA mutations inside a cell.
Last Revised: 01/27/2016