CT Scans and Lung Cancer Small or slow-growing nodules (小结节) discovered on a lung scan are unlikely to develop into tumors over the next two years, researchers reported on Wednesday. The findings reported in the New England Journal of Medicine, could help doctors decide when to do more aggressive testing for lung cancer. They could also help patients avoid unnecessarily aggressive and potentially harmful testing when lesions (损伤) found. Lung cancer, the biggest cancer killer in the United States and globally, is often not diagnosed until it has spread. It kills 159,000 people a year in the United States alone. The work is part of a larger effort to develop guidelines to help doctors decide what to do when such growths, often discovered by accident, appear in a scan. High-tech X-rays called CT scans can detect tumors-but they see all sorts of other blobs (模糊的一团) that are not tumors, and often the only way to tell the difference is to take a biopsy (活检), a dangerous procedure. At the moment, routine lung cancer screening is considered impractical because of its high cost and because too many healthy people are called back for further testing. Good guideline could help make lung cancer screening practical, Dr. Rob van Kiaveren of the Erasmus Medical Center in Rotterdam, the Netherlands, who led the new study, said in a telephone interview. The team looked at 7, 557 people at high risk for lung cancer because they were current and former smokers. All received multidetector (多层螺旋) CT scans that measured the size of any suspicious-looking modules. Volunteers who had nodules over 9.7 mm in width, or had growth of 4.6 mm that grew fast enough to more than double in volume every 400 days, were sent for further testing. Of the 196 people who fell into that category, 70 were found to have lung cancer, 10 additional cases were found years later. But of the 7, 361 who tested negative during screening only 20 lung cancer cases later developed. In a second round of screening done one year after the first, 1.8 percent were sent to the doctor because they had a nodule that was large or fast-growing. More than half turned out to have lung cancer. The result means that if the screening test says you don’t have lung cancer, you probably don’t, the researcher said. "The chances of finding lung cancer one and two years after a negative first-round test were 1 in 1,000 and 3 in 1,000 respectively, "they concluded. The new study indicates that in case of small or slow-growing lung nodules______.

A. you cannot be too careful
B. cancer is just matter of time
C. a biopsy is unnecessary
D. more aggressive testing is a must