The role of inflammation in the genesis of cancer is a complex and seemingly paradoxical issue. As mentioned in last week’s health tip, inflammation is part of a process that helps the body remove damaged cells, irritants or germs following injury, exposure or infection. Cancer cells generally fall into the “damaged cells” category and are destroyed by an inflammation-stimulated immune system. In some cases, however, particularly when the inflammation becomes persistent, the opposite occurs and inflammation contributes to the development of cancer.
Cancer can also develop from chronic infection. Infection, in contrast to inflammation, is caused by an organism, such as bacteria, viruses, or fungi. An inflammatory response is one of the steps that the body normally takes to rid itself of an infection. When certain infections become chronic, however, the associated persistent inflammation may set the stage for the development of cancer.
Recently, research has shed some light on how inflammation could lead to the development of cancer. Inflammation can cause a drop in several proteins that are involved in DNA repair. This leads to a higher rate of gene mutations, some of which are responsible for cancer development. The following are a few of the most well-known cancers that have persistent inflammation as an associated cause.
Colon cancer: High fat diets, sedentary life style, genetic factors, and cigarette smoking are known to be the most common causes of colon cancer. However, two inflammatory conditions of the bowel—ulcerative colitis and Crohn’s disease (both of unknown causes)—are also known to impose an increased risk of developing colon cancer. Whereas, most colon cancer begins as a small growth called a polyp, colon cancer associated with inflammatory bowel disease typically involves larger areas of the colon, often necessitating removal of the entire colon for treatment.
Cervical/Throat Cancer: Cervical cancer, occurring in the lower portion of the female uterus, is usually caused by a human papillomavirus (HPV) infection. Over half of the cases of throat cancer are also related to this infection. Most HPV infections are cleared by the body. When the body’s immune system is unable to get rid of a high-risk HPV infection, it becomes chronic and can lead to the development of cancer.
Liver cancer: Long term alcohol abuse can lead to irreversible scarring of the liver, a condition known as cirrhosis. The combination of alcoholism and cirrhosis is known to increase one’s risk of developing liver cancer. This increased risk, however, is small in comparison to the risk imposed by chronic viral hepatitis. Worldwide, chronic hepatitis B and C are responsible for 80% of cases of liver cancer, resulting in thousands of deaths each year. Unfortunately, chronic hepatitis, particularly that caused by the hepatitis C virus, can go undetected for years.
Stomach cancer: A bacterial infection of the lining of the stomach wall caused by Helicobacter pylori (H. pylori) is a well-known cause for ulcer symptoms. This same infection has been found to double the risk of developing cancer of the stomach. Although not yet proven, it is believed that treatment of the bacterial infection with a combination of antibiotics is effective in eradicating this risk.
Lung cancer: Worldwide, over one million people die from lung cancer each year. Up to 90% of this cancer can be attributed to cigarette smoking. One of the major factors in the development of lung cancer is inflammation brought on by repeated exposure to tobacco smoke. Other lung irritants, including silica dust, asbestos and coal dust, also appear to promote the development of lung cancer through an inflammatory pathway.
Having a disease or risk factor associated with the development of an inflammation-related cancer does not mean that cancer is inevitable. It does mean that the odds of cancer occurrence are higher and that special measures should be taken to reduce the risk, or to detect the cancer in as early a stage as possible. The relationship between inflammation and cancer is the subject of ongoing research. Important issues to be addressed in the future include:
- Developing vaccines for infectious diseases associated with chronic inflammation. Hepatitis B vaccine is currently available and a hepatitis C vaccine is in development. The HPV vaccine holds promise to further reduce the incidence of HPV-related cancers.
- Detecting asymptomatic disease, such as H. pylori infection of the stomach or hepatitis C, so that early treatment can be offered.
- Learning how often and how best to screen for certain cancers. It has been determined that the longer someone has a chronic inflammatory condition, the greater the likelihood of developing cancer. Information like this is taken into account when considering appropriate screening intervals.
- Developing medications to reduce inflammation. There is some evidence to support taking aspirin to prevent colon cancer in certain individuals. Additionally, the non-steroidal anti-inflammatory medicine, celecoxib, can reduce the number of pre-cancerous polyps that develop in patients with a condition known as familial adenomatous polyposis.
- Encouraging preventive measures, for example smoking cessation, when an unhealthy habit is clearly related to the inflammatory cancer.