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Swensen and colleagues at the Mayo clinic have performed a retrospective cohort study on 100 patients with solitary pulmonary nodules (SPN) that measure between 4 and 30 mm in diameter. The patient cohort was 629 patients; 320 men and 209 women, who all had new and recently discovered 4 to 30 mm SPNs (all radiologically indeterminate). By looking at clinical data, including age, gender, cigarette smoking status, history of extrathoracic malignant cancer, asbestos exposure, chronic interstitial, or obstructive lung disease, as well as chest x-ray data, such as diameter, location, spiculation, and shagginess or cavitation, they were able to develop cancer predictors in two-thirds of the patients. These predictors were then tested on the other third of the patients, and it was discovered through multivariate logistic regression to accurately estimate the probability of malignancy.
After the statistical analysis, the three specific clinical characteristics of age, cigarette smoking, and history of cancer five or more years ago, as well as the three radiologic characteristics of diameter, spiculation, and upper lobe location of the SPN, were all independent predictors of cancer.
There are approximately 150,000 SPN identified on U.S. x-rays per year. In an active teaching hospital such as ours, it seems that we get more than our fair share. Clearly, any clinician’s office gets a number of these a year. What to do with them has always been the problem. If they are less than 4 mm, repeating a chest x-ray is probably what is done, especially if it’s a symptomatic patient. If they are greater than 30 mm, aggressive work-up is usually fruitful. The dilemma has always been what to do between these two sizes. Armed with the knowledge that a majority of these result from benign conditions, leaving them alone may be an option, since the percentages show that 55% are from granulomas and 4% are from benign tumors. Unfortunately, that leaves 40% or less being malignant. With further diagnostic evaluation, including possible tomograms, computer tomography (CT), sputum cytologic exam, bronchoscopy, or transthoracic needle aspiration biopsyall coordinated by either a pulmonologist or a surgeonwe’d all love to have a way to decide whether to proceed in a work-up of these patients.
Swensen et al have given us a way. Following the literature, they found 65% of their nodules were benign, 23% were malignant, and 12% were indeterminate. The clinical characteristics that predicted malignancy included cigarette smoking, history of cancer, diagnosis five or more years ago, and older age. Three radiologic characteristics stood out as predictors of cancer: larger diameters, spiculation present on the film, or upper lobe location. But the most powerful aspect about this study is that they were independent predictors of malignancy. If all were present, presumably some would have a significant risk of cancer. As a matter of fact, in their study, this would approach 98% if the lesion were 30 mm in someone 75 years old.
I, for one, will be looking at these clinical and radiologic characteristics when I see an indeterminate SPN. It will help me better gauge in discussions with the patient whether to proceed with aggressive work-up of the SPN.