Researchers at Johns Hopkins led a proof-of-principle study that successfully identified tumor DNA shed into the blood and saliva of 93 patients with head and neck cancer. Their report (“Detection of somatic mutations and HPV in the saliva and plasma of patients with head and neck squamous cell carcinoma”) is published in Science Translational Medicine.
"We have shown that tumor DNA in the blood or saliva can successfully be measured for these cancers," says Nishant Agrawal, M.D., associate professor of otolaryngology and of oncology at the Johns Hopkins University School of Medicine. "In our study, testing saliva seemed to be the best way to detect cancers in the oral cavity, and blood tests appeared to find more cancers in the larynx, hypopharynx, and oropharynx. However, combining blood and saliva tests may offer the best chance of finding cancer in any of those regions."
Dr. Agrawal explains that inborn genetic predispositions for most head and neck cancers are rare, but other mutations that don't generally occur in normal cells have long been considered good targets for screening tests. In the case of head and neck cancers associated with human papillomavirus (HPV) Dr. Agrawal and his colleagues searched patients' blood and saliva samples for certain tumor-promoting, HPV-related DNA. For non-HPV-related cancers, which account for the worldwide majority of head and neck tumors, they looked for mutations in cancer-related genes that included TP53, PIK3CA, CDKN2A, FBXW7, HRAS, and NRAS.
The major risk factors for head and neck cancers are alcohol, tobacco, including chewing tobacco, and HPV infection.
For the study, 93 patients with newly diagnosed and recurrent head and neck cancer gave saliva samples, and 47 of them also donated blood samples before their treatment at The Johns Hopkins Hospital and MD Anderson Cancer Center in Texas. The scientists detected tumor DNA in the saliva of 71 of the 93 patients (76%) and in the blood of 41 of the 47 (87%). In the 47 who gave blood and saliva samples, scientists were able to detect tumor DNA in at least one of the body fluids in 45 of them (96%).
When the scientists analyzed how well their tumor DNA tests found cancers in certain regions of the head and neck, they found that saliva tests fared better than blood tests for oral cavity cancers. All 46 oral cavity cancers were correctly identified through saliva tests, compared with 16 of 34 oropharynx cancers (47%), seven of 10 larynx cancers (70%), and two of three hypopharynx cancers (67%).
The oral cavity refers to areas within the mouth, including the lips, front of the tongue, cheeks and gums. The oropharynx and hypopharynx are located in the back of the throat. The larynx, also in the throat, is typically known as the voice box.
"One reason that saliva tests may not have been as effective for cancer sites in the back of the throat is because we didn't ask patients to gargle; we only asked them to rinse their mouths to provide the samples," says Dr. Agrawal, a member of Johns Hopkins' Kimmel Cancer Center and Ludwig Center.
Blood tests correctly identified tumor DNA more often in 20 of 22 oropharynx cancers (91%), six of seven larynx cancers (86%), and all three hypopharynx cancers. Taken together, blood and saliva tests correctly identified all oral cavity, larynx, and hypopharynx cancers and 20 of 22 oropharynx cancers (91%).
Dr. Agrawal points out that the sensitivity of the tests overall depended on the cancer site, stage and HPV status, ranging between 86 to 100%. He also reports that saliva tests performed better for early-stage cancers, finding all 20 cancers, compared with blood tests that correctly identified seven of 10. He and his team found the opposite was true for late-stage cancers: Blood tests found more late-stage cancers (34 of 37), compared with saliva tests (51 of 73). Blood tests also correctly identified HPV-related tumors, occurring in 30 of the 93 patients, more often than saliva tests, probably because HPV-related tumors tend to occur in the back of the throat, which may not have been reached with the saliva rinse.
"Our ultimate goal is to develop better screening tests to find head and neck cancers among the general population and improve how we monitor patients with cancer for recurrence of their disease," says Bert Vogelstein, M.D., the Clayton Professor of Oncology at the Johns Hopkins Kimmel Cancer Center, co-director of the Ludwig Center at Johns Hopkins and a co-author of the study.
The scientists caution that further study of their tumor DNA detection method in larger groups of patients and healthy people is needed before clinical effectiveness can be determined, and that refinements also may be needed in methods of collecting saliva and the range of cancer-specific genes in the gene test panel.
In addition, according to Dr. Agrawal, "We don't yet have definitive data on false positive rates, and won't until there are more studies of the tests in healthy people." However, he notes, the formulas used to analyze their blood and saliva tests are designed to weed out questionable result.