Saliva Test May Spot Mouth Cancer Early
In the lab, it predicted more than 80 percent of cases, researchers say
THURSDAY, July 7, 2005 (HealthDay News) -- Oral cancer patients may have increased levels of certain bacteria in their saliva, new research has found, and detecting those bacteria may help diagnose the disease in its earlier and more curable stages.
"Many researchers are working on a saliva test for oral cancer," said Donna Mager, an assistant professor at the Forsyth Institute in Boston and lead author of the study, published online Wednesday in the Journal of Translational Medicine. She said her team's efforts are unique in that they are focusing on "bacteria that grow in the mouth as possible markers for oral cancer."
The research is already proving fruitful: Mager's group was able to predict with 80 percent accuracy which patients had oral cancer by examining three specific species of bacteria.
Other researchers, she said, "are looking at protein and genetic material that indicate that certain cancer-causing genes have been turned on. Or they are looking at inflammatory mediators or signs of inflammation that may indicate there is cancer present."
To detect specific bacteria, Mager's team first collected saliva samples from 45 people diagnosed with oral squamous cell cancer, and compared those samples to samples from 45 healthy individuals matched for age, gender and smoking status -- a risk factor for oral cancer.
The researchers then analyzed the saliva samples for levels of 40 different bacteria species, using bacterial DNA probes.
Six of the 40 different bacteria were found to be significantly higher in cancer patients compared to healthy subjects, Mager said, "but only three were predictive of the presence of cancer."
The three included Capnocytophaga gingivalis, Prevotella melaninogenica and Streptococcus mitis, she said.
"What we find is, when the DNA is above a certain threshold, these three bacteria [species] become diagnostically sensitive," she said.
How might bacteria signify the presence of malignancy? "Our theory is that in [cancer's] very initial stages, when cells are beginning to change, there is a shift in the colonization of the bacteria before the cells change," Mager said. The test appears to detect the bacteria once they have undergone this shift in colonization, she said.
"In general bacteria are resistant to changes," she said. "But when you get a major effect like DNA changes in cells and changes in the receptors [on the surfaces of the cells], then you will get a significant change in the bacteria."
Squamous cell cancer accounts for 90 percent of all oral malignancies. Average five-year survival rate for this form of the disease is just 54 percent -- lower than many other major cancers, Mager said. About 400,000 new cases are diagnosed each year worldwide, she said.
Risk factors include tobacco and alcohol use. The two in combination are especially powerful in promoting oral cancers, Mager said..
David T. Wong, associate dean of research at the University of California, Los Angeles School of Dentistry, is also working on an early detection saliva test for oral cancer -- one that focuses on genetic material called messenger RNA. He praised the new study.
"This is an important study that supports the potential utility of oral microbes to diagnose oral cancer in saliva," Wong said. "Microbial diagnostics will and should add another dimension of information for oral cancer screening and diagnostics."
The study findings could also help researchers better understand the development of oral cancers, he said.
The study was a part of a collaboration among the Forsyth Institute, Dana Farber Cancer Institute and Massachusetts General Hospital.
To learn more about oral cancers, visit the American Cancer Society.