‘Screening for Lung Cancer; Time to Think Positive’, Dr David Milne, Lancet, Vol 354, 1999
27th November 2006 5:26PM
Background
Lung cancer is a leading cause of death amongst smokers in this country, as it is around the world. The cure rate for lung cancer is 12% and the 5-year survival is only slightly better than this. Interestingly, the 5-year survival rate for stage 1 lung cancer treated by surgery is 70%. This data suggests that survival in lung cancer may be substantially improved by early detection through a screening program and surgical intervention. Several randomized trials in the 1970's using chest radiographs as a screening tool have not convincingly shown a beneficial effect on mortality.
The study
Results from The Early Lung Cancer Action Project (ELCAP) were published in the July 10, 1999 of The Lancet. This study was designed to evaluate baseline and annual repeat screening by low-radiation-dose CT in people who have a high risk of lung cancer. This first announcement of results is from the baseline experience.
The study is a collaboration between New York Medical Centre and McGill University Montreal Canada. 1000 symptom free volunteers were enrolled in the trial. All of those enrolled were aged 60 years or over, all had smoked at least 10 years and had no prior history of malignancy. Chest Radiographs and low dose CT were performed in all patients.
CT imaging was performed on a helical scanner with the whole of both lungs imaged in a single breath-hold (about 15-20 seconds). The dose used for the scans was approx. 20% of the standard radiation dose for a helical chest CT examination and no intravenous contrast was used. If low-dose CT showed benign calcifications in terms of extent or distribution, within a nodule with smooth edges and size of less than 20mm, the nodule was classified as benign. When non-calcified nodules were detected on low-dose CT, a standard-dose diagnostic CT of the chest with high resolution imaging of the nodule or nodules was performed. If the high resolution images of the nodule(s) did not show benign features, the ELCAP protocol recommended further investigation according to the size of the nodule.
5mm or less were followed up in 3 months time, and if there had been no change, repeat limited CT at 6 months, 12 months and 24 months. If no growth was noted over 2 years, the nodule was classified as benign.
6-10mm in size the nodule was assessed on an individual basis as to whether biopsy was possible. If no biopsy was possible follow-up for growth as described was performed.
11mm or more in size, biopsy was performed.
Non-calcified nodules were detected in 233 (23%) of participants by low-dose CT at baseline compared to 68 (7%) by chest x-ray. Malignant disease was detected in 27 (2.7%) by CT and 7 (0.7%) by CXR. Of the 27 CT detected cancers, 26 were resectable. Biopsies were performed on 28 of the 233 participants with non-calcified nodules. Of these, 27 were malignant and one was benign.
Comment:
Although this study is in its infancy, it is apparent that low-dose CT can greatly improve the detection rate for small non-calcified nodules in the lungs and thus of lung cancer at an earlier and potentially more curable stage. Although false positive results are common, they can be managed with little use of invasive diagnostic procedures. The radiation burden for this form of CT screening approximates that of a chest radiograph and the cost of the CT procedure is less than that of a standard chest CT examination.
Despite the acknowledgement that this paper represents work in progress, some doctors may wish to advise their high-risk patients of this new screening technique, which may prove to have a higher yield than mammography in breast cancer screening..
