US scientists have found human saliva carries markers of breast cancer and have opened the door to the possibility that one day your doctor, or even your dentist, could do a simple saliva test for the disease.

The discovery, published in the January issue of Cancer Investigation, was the work of researchers at The University of Texas Health Science Centre, Houston (UTHSC).

They found that the appearance of breast cancer changes the mix of proteins secreted by the salivary glands. A person with breast cancer secretes a different profile of proteins compared to a person without, claim the researchers.

Professor of diagnostic sciences at UTHSC, Dental Branch, Dr Charles Streckfus, an expert on human saliva and molecular epidemiology, led the study.

The researchers compared the saliva from three pooled samples, each taken from 10 patients. One sample was from patients who had benign breast tumours, another from patients who had malignant breast tumours (ductal carcinoma in situ, DCIS), and the third was a control sample from healthy patients with neither condition.

The researchers looked for differential protein variations using isotope tagging. They compared the two tumour groups to the healthy control groups.

Streckfus and colleagues found about 130 proteins altogether, with 49 expressed differently between the healthy control pool and the two tumour pools.

They also found unique proteins for a tumour called fibroadenoma, the most common type of benign breast tumour. This is a unique finding, said Streckfus, "as it targets both the benign and malignant tumour, which could potentially reduce the number of false positives and false negatives associated with current cancer diagnostics".

Streckfus and colleagues concluded that:

"The study suggests that saliva is a fluid suffused with solubilised by-products of oncogenic expression and that these proteins may be modulated secondary to DCIS. Additionally, there may be salivary protein profiles that are unique to both DCIS and fibroadenoma tumors."

The research is now being applied to a technology called "lab on a chip", which basically opens up the possibility that one day, a dental practice or other health care facility, will be able to carry out a diagnostic test that detects the presence of cancer before the tumour forms.

Co-researcher William P.Dubinsky said saliva could be the key to many medical secrets:

"Saliva is a complex mixture of proteins. We go through a process that compares different samples by chemically labeling them in such a way that we can not only identify the protein, but determine how much of it is in each sample," explained Dubinsky.

"This allows us to compare the levels of 150-200 different proteins in cancerous versus non-cancerous specimens to identify possible markers for disease," he added.

Screening for breast cancer currently involves use of ultrasound, mammograms, biopsies, and blood tests. The researchers in this study hope that one day that list will include salivary diagnostics, possibly carried out during routine trips to the dentist.