Smokers and ex-smokers who receive regular CT lung cancer checkups will probably not present with suspicious masses. But any lung nodules that are found are likely to be cancerous.
The Early Lung Cancer Action Project studied 1000 high-risk subjects who received annual low-dose CT screening for lung cancer, uncovering dramatic differences in first- and second-year results, according to Dr. Claudia Henschke, the principal investigator. Only about 1.5% of patients showed lung masses in the second year, but 43% of these masses were malignant, and 83% of the malignancies were stage IA cancers.
In contrast, baseline studies performed on the same patients in the previous year had uncovered suspicious masses in 23% of the exams. About 12% of the suspicious nodules involved malignancy, and 82% of the cancers found were still at an early stage, Henschke said.
The ELCAP trial recruited symptom-free volunteers who were at least 60 years old and had smoked the equivalent of a pack of cigarettes a day for 10 years. Overall, the trial has identified 66 lung cancer cases.
Henschke, chief of chest imaging at Weill Medical College of Cornell University in New York City, described the results at the annual meeting of the International Society for Strategic Studies in Radiology last week in San Francisco. They were also published in the July 1 issue of Cancer.
The key to the diagnostic power of low-dose CT screening continues to be its ability to uncover early stage lung cancer, according to Henschke. Typically, only 7% of lung cancers found after a physical examination and a diagnostic chest x-ray are stage I, she said. Cancer survival statistics from the National Cancer Institute's SEER database indicate that one in two individuals are still alive five years after they are diagnosed with a lung tumor that is less than 1 cm in diameter. The odds of five-year survival drop to one in five when the tumor is larger than 3 cm.
Henschke has also discovered that CT can be used to noninvasively classify lung nodules as solid, partially solid/nonsolid, and nonsolid. Each class has a different propensity for cancer:
- Solid nodules have a malignancy rate of 7%.
- Partially solid/nonsolid nodules have a malignancy rate of 63%.
- Nonsolid nodules have a malignancy rate of 18%.
Nodule size also requires consideration, however.
"When you standardize for size, you find that solid and nonsolid nodules have equal frequency of malignancy at baseline compared with the partially solid/nonsolid ones, so these are individuals who need much more attention," Henschke said.
An analysis of the data indicates that the program cost about $2500 per life-year saved. Smoking cessation education should be linked to local CT lung cancer screening programs, according to Henschke. In addition to the ELCAP trial, she is associated with the 11-hospital New York Early Lung Cancer Project and an international study that involves 10 U.S. and 10 foreign testing sites. She estimates that 44,000 people worldwide have been screened for lung cancer with the low-dose CT protocol.
-- By James Brice
