DNA shed from human head and neck tumours detected in blood and saliva for the first time.
On the hunt for better cancer screening tests, Johns Hopkins researchers led a proof of principle study that successfully identified tumour DNA shed into the blood and saliva of 93 patients with head and neck cancer. The team state that they have shown that tumour DNA in the blood or saliva can successfully be measured for these cancers. The data findings showed that 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, the team state that combining blood and saliva tests may offer the best chance of finding cancer in any of those regions. The study is published in the journal Science Translational Medicine.
Previous studies show that inborn genetic predispositions for most head and neck cancers are rare, however other mutations that don’t generally occur in normal cells have long been considered good targets for screening tests. The major risk factors for head and neck cancers are alcohol, tobacco, including chewing tobacco, and HPV infection. These type of cancers occur in more than 50,000 people in the U.S. each year. In the case of head and neck cancers associated with HPV the current study analysed patients’ blood and saliva samples for certain tumour-promoting, HPV-related DNA. For non-HPV-related cancers, which account for the worldwide majority of head and neck tumours, the researchers looked for mutations in cancer-related genes that included TP53, PIK3CA, CDKN2A, FBXW7, HRAS and NRAS.
For the current 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 team detected tumour DNA in the saliva of 71 of the 93 patients (76 percent) and in the blood of 41 of the 47 (87 percent). In the 47 who gave blood and saliva samples, scientists were able to detect tumour DNA in at least one of the body fluids in 45 of them (96 percent).
When the researchers analyzed how well their tumour 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 percent), seven of 10 larynx cancers (70 percent) and two of three hypopharynx cancers (67 percent).
The team explain that 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. They go on to add that one reason that saliva tests may not have been as effective for cancer sites in the back of the throat is because they didn’t ask patients to gargle; the researchers state that they only asked them to rinse their mouths to provide the samples.
The results showed that blood tests correctly identified tumour DNA more often in 20 of 22 oropharynx cancers (91 percent), six of seven larynx cancers (86 percent) 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 percent).
In the current study the sensitivity of the tests overall depended on the cancer site, stage and HPV status, ranging between 86 to 100 percent. The data findings show that saliva tests performed better for early-stage cancers, finding all 20 cancers, compared with blood tests that correctly identified seven of 10. 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). The findings also showed that blood tests correctly identified HPV-related tumours, occurring in 30 of the 93 patients, more often than saliva tests, probably because HPV-related tumours tend to occur in the back of the throat, which may not have been reached with the saliva rinse.
The team state that the ultimate goal is to develop better screening tests to find head and neck cancers among the general population and improve how patients with cancer are monitored for recurrence of their disease. They go on to add that further study of their tumour 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, the researchers stress that they 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, they note that the formulas used to analyze their blood and saliva tests are designed to weed out questionable results.
Previous studies show that false results in gene tests arise when DNA are copied many times, sequenced and analyzed. The current study used a method they developed and tested previously in cervical fluid to find ovarian and cervical cancers. Specifically, the lab attach a kind of genetic bar code, a random set of 14 DNA base pairs, to trace or ‘file’ each copied DNA fragment to its original one. DNA copies lacking the bar code are suspected to be an artifact of the process, and any mutation found in it is disregarded.
The researchers surmise that to screen for head and neck cancers doctors conduct physical examinations with biopsies taken of suspicious-looking lesions. However, the team state that this method is not ideal, as evidenced by the fact that most head and neck cancers are rarely found at very early stages, when they are most curable. They go to note that their test if used commercially, likely would cost several hundred dollars therefore their future long-term goal is to create a test that costs less than $50 so it can be administered by physicians or dentists.