The UCLA School of Dentistry continues to blur the boundaries between medicine and dentistry. Research is ongoing in the field of salivanomics: the diagnosis of diseases through analysis of saliva. In the future, it is likely that a number of serious illnesses, such as cancers, can be diagnosed by examining a saliva sample rather than an invasive, painful biopsy that may require expertise to perform. The findings were published in a recent edition of the Journal of Biological Chemistry.
Pancreatic cancer is the fourth most common cause of cancer-related deaths in the United States. Many individuals with the disease die within one year of diagnosis and only 6% survive for five years. Apple Computer founder Steve Jobs survived longer than most victims—seven years. He received extensive treatment, including a liver transplant. A major factor increasing the mortality of pancreatic cancer is that it is often not diagnosed until it grows to an advanced stage. Thus, early diagnosis with a saliva test could likely increase survival.
A research team led by Dr. David Wong, the dentistry school's associate dean of research, studied a mouse model with pancreatic cancer. They were able to identify biomarkers for the cancer in the saliva. (A biomarker, or biological marker, refers to a measured characteristic which may be used as an indicator of some biological state or condition.) The researchers note that, to date, salivary biomarker panels have been successfully developed for cancers of the breast, ovaries, lungs, and pancreas. However, salivanomics researchers are still in the process of determining how biomarkers produced by other parts of the body ultimately appear in the mouth. It has been theorized that RNA molecules, which translate the genetic code from DNA to produce protein, are secreted into fluid surrounding the cells; thus, they can act as an information signal system that can transmit information between cells.
The research team employed this theory in the mouse model and were able to demonstrate that tumor-derived extracellular RNA molecules are transported through small structures within the cells known as exosomes; the exomes stem from the source of the tumor and are subsequently re-processed into saliva as biomarkers. The investigators proved this theory by examining the saliva of mice that contained biomarkers for pancreatic cancer. To prove it, the researchers examined mice models with pancreatic cancer whose saliva showed evidence of biomarkers for pancreatic cancer. When they blocked the production of exosomes at the source of the tumor, they found that the pancreatic cancer biomarkers no longer appeared in the mouse's saliva.
Dr. Wong explained, “This paper is significant because it provides credibility to the mechanism of systemic disease detection in saliva. We have been able to substantiate the biological connection between systemic disease and the oral cavity.”
- Risk factors for pancreatic cancer include:
- Age: Most pancreatic cancer occurs in people over the age of 55.
- Smoking: Heavy cigarette smokers are two or three times more likely than nonsmokers to develop pancreatic cancer.
- Obesity and physical inactivity: Pancreatic cancer is more common in people who are very overweight and in people who don't get much physical activity.
- Diabetes: Pancreatic cancer occurs more often in people who have type 2 diabetes than in those who do not.
- Gender: More men than women are diagnosed with pancreatic cancer.
- Race. African-Americans are more likely than Asians, Hispanics, or whites to be diagnosed with pancreatic cancer.
- Family history: The risk for developing pancreatic cancer is higher if a person's mother, father, or a sibling had the disease.
- Cirrhosis of the liver: People with cirrhosis have a higher risk of pancreatic cancer.
- Workplace exposures. Exposure to certain occupational pesticides, dyes, and chemicals used in the metal industry may increase the risk of pancreatic cancer.
- Some genetic syndromes: Certain inherited gene mutations, such as in the BRCA2 gene, increase the risk of pancreatic cancer.
- Chronic pancreatitis: Long-term inflammation of the pancreas has been linked with increased risk for pancreatic cancer.
Take home message:
If this research progresses to a reliable test for humans, it could ultimately lead to screening tests done painlessly using saliva for a myriad of cancers. The test could be conducted in a medical or dental office—it could also be taken at home; the sample could then be sent to a lab for analysis.