By Karla Gale
NEW YORK (Reuters Health)—A blood test to measure autoantibodies to tumor-associated antigens (AABT) can help diagnose lung cancer—even in the early, asymptomatic stage—according to several presentations this week at CHEST 2010, the annual meeting of the American College of Chest Physicians in Vancouver.
The EarlyCDT-Lung test (Oncimmune LTD) can detect both small cell and non-small cell lung cancer, the investigators report, and when used along with computed tomography (CT), provides a cost-effective screening test among people at high risk due to long-term smoking.
The EarlyCDT-Lung test includes eight tumor antigens and has a sensitivity of 40% and specificity of 93% for lung cancer in high-risk people, Dr. John Robertson, professor of surgery at Nottingham University, England, and chief scientific officer of Oncimmune, told Reuters Health. "Compared with CT, EarlyCDT-Lung has 3 times the positive predictive value and 7 times fewer false positives."
In comparison, he said, testing for prostate specific antigen has a sensitivity of 33% and specificity of 86% for prostate cancer, while the values for mammograms are 40% and 92%, respectively, for breast cancer.
To determine AABT's positivity rate by stage of disease and histological subtype, Dr. Peter Boyle, from the International Prevention Research Institute in Lyon, France, and colleagues tested serum from 842 diagnosed patients prior to treatment.
For small cell lung cancer, the positivity rate was 49.4% for limited disease and 53.1% for extensive disease. Positivity for non-small cell lung cancer ranged from 28.0% in stage 1 to 34.4% in stage 4. Rates were similar for each subtype of non-small cell cancer (adenocarcinoma, large cell, and squamous).
In another study at the conference, Dr. Caroline Chapman, from the University of Nottingham, and her team showed that autoantibodies to tumor-associated antigens may be present even before the clinical diagnosis of small cell lung cancer. They could do this because small cell lung cancer is present in about half of patients with Lambert-Easton myasthenic syndrome (LEMS), an autoimmune neuromuscular disorder.
They tested serum samples from 69 individuals with LEMS with lung cancer (of which 18 were available months before their cancer diagnosis), 103 with LEMS without lung cancer during at least 3 years of follow-up, and 172 age-and gender-matched controls.
The researchers found tumor autoantibodies in 57% of the lung cancer patients, including 50% of patients prior to their diagnosis, and in 60% within the next month.
The autoantibodies were present in 15% of LEMS patients without cancer, similar to the frequency in the control subjects.
"These results show that the presence of tumor autoantibodies in patients with lung cancer may provide an early signal of disease for high-risk individuals, when the chance of successful treatment would be greatest," Dr. Robertson said.
Dr. Boyle's team also estimated the cost-effectiveness of using AABT to screen high-risk patients. Their model compared four screening strategies: AABT followed by CT if positive (AABT --> CT), AABT plus CT at the same time (AABT + CT), CT alone, and no screening. Estimated costs were $300 for an AABT and $301 for a CT.
The cost-effectiveness of AABT --> CT vs. no screening was greatest, at $13,830 per quality-adjusted life year (QALY) saved.
Corresponding values per QALY were $17,582 for ABBT+CT vs. CT alone, $24,473 for ABBT+CT vs. no screening, and $31,158 for CT alone vs. no screening.
"A positive AABT shows that a patient is at much higher risk than the clinician thought before" and should undergo further workup, Dr. Robertson said. If the positive AABT is followed by a negative CT scan, he advised that CT be repeated within the next year.
"But the AABT does not pick up all lung cancers, so just because the initial test is negative does not mean the patient is at lower risk, and the doctor should continue to follow-up as before," he added.
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