Could a blood test detect lung cancer early?

Blood tests that hunt for an enzyme that spikes in patients with non-small-cell lung cancer may offer a cheaper and more reliable way to find and treat the nation’s top cancer killer, a new study suggests.

A study published this week in the journal Clinical Cancer Research says the enzyme isocitrate dehydrogenase 1 (IDH 1) can be readily detected in the blood of patients with early non-small-cell lung cancer. The newly identified “biomarker” may offer a means of screening for lung cancer with fewer false positives than low-radiation CT scans, which have recently come into broad use to screen for the disease.

The Chinese researchers conducted blood tests on close to 1,000 patients already diagnosed with lung cancer and an additional 500 healthy control patients. By looking for high levels of IDH 1 alone, the researchers were able to detect non-small-cell lung cancer in roughly 76.2% of subjects who had lung cancer. And all but 23% of those who tested positive for lung cancer by that measure did, in fact, have the disease.

This combination of what cancer researchers call “sensitivity and specificity” -- the ability to accurately detect disease without high rates of false positives -- makes testing the blood for IDH 1 a plausible alternative to low-dose CT scanning for smokers and those deemed at high risk of developing lung cancer.

Though CT scanning is able to detect lung cancer with high reliability in those who have it, 96.4% of those who turned up worrisome findings were not, in fact, sick. That makes it important to find an adjunct or a cheaper alternative to CT scanning that results in fewer false positives.

Testing the blood for IDH 1 is inexpensive, does not require a high level of laboratory expertise, and requires a small amount of blood, the researchers said. And the measure can be made even more reliable in diagnosing lung cancer if labs also look for three other cancer markers alongside IDH 1, the researchers concluded.