The protein, called tNOX, is the first tumor marker for all cancers ever described, says D. James Morre, PhD, distinguished professor of medicinal chemistry at Purdue University in West Lafayette, Ind.
"If tNOX is present, cancer is present," he tells WebMD. "Presumably, the more there is, the worse the disease."
Putting tNOX to the Test
Normal cells have the NOX enzyme only when they are dividing in response to growth hormone signals. In contrast, cancer cells have NOX activity at all times.
This overactive form of NOX, known as tNOX -- for tumor-associated NOX -- has long been thought to be vital for the growth of cancer cells because drugs that inhibit tNOX activity also block tumor cell growth.
In two new studies presented here at a meeting of the American Association for Cancer Research, Morre and colleagues put the protein to the test.
It passed with flying colors, he says.
Test Predicts Prostate Cancer Progression
The first study involved 19 men with advanced metastatic prostate cancer.
The researchers found that the nine men whose prostate cancer continued to progress -- based on their PSA levels, a blood test elevated in most men with prostate cancer -- had 60% more tNOX in their blood compared with the 10 men with stable or falling PSA levels.
"It's the first demonstration that we have, assuming that PSA levels indicate major tumor burden in some fashion, that there is a really good correlation between tNOX levels and response to therapy," Morre says.
He believes the test will be even more useful than PSA. The reason: A man can have high PSA levels and not have cancer. The tNOX enzyme, on the other hand, is only present if there is cancer.
Test Spots Lung Cancer
The second study looked at tNOX levels in 421 volunteers, including people with lung cancer, smokers who had not been diagnosed with lung cancer, and healthy individuals.
Among the 104 people with lung cancer, 103 tested positive for tNOX. In smokers older than 40, 12% were positive, which Moore says is about the normal rate of lung cancer picked up with high resolution CT scanning.
But, in contrast, none of the 25 healthy people tested positive.
Morre says he envisions using a tNOX test as a screening tool for the early detection of lung cancer in high-risk people. Currently, there is no test able to reliably diagnose lung cancer early, when it is most treatable.
"All heavy smokers over age 50 should be tested for tNOX," he tells WebMD. Those who test positive would then be followed up with a medical examination and further tests.
A weak signal would indicate early cancer at a stage where it is potentially curable, he adds.
tNOX May be Useful in Other Cancers, Too
The next step is to look at tNOX levels in people with other types of cancer, the researchers say.
Lorraine O'Driscoll, PhD, a cancer researcher at Dublin City University in Ireland, says that while the test could be extremely useful, she imagines tNOX will be used as part of a panel of markers to detect cancer and monitor its progression.
"There are so many potential candidates out there that I doubt any one will prove to be the one answer," she tells WebMD. "Rather, we will probably use a combination of markers and tNOX could certainly prove to be one of them."