Should chest CT be used to screen for lung cancer?

Lung malignancy is the #1 cause of cancer death in theUnited States.  In 2011, approximately 221,130 patients (115,060 men and 106,070 women) are estimated to be diagnosed with this malignancy.  An estimated 156,940 people (85,600 men and 71,340 women) will die of this disease this year.  Although cigarette use has decreased, we still have inAmericaabout 94 million current or former smokers who are at increased risk of developing lung tumors.

In the past, screening high risk but asymptomatic smokers has been ineffective with chest x-ray, with or without sputum cytology.  However, a new study shows that screening with low dose chest CT reduces lung tumor death by 20%, in comparison to screening with chest x-ray alone (The National Lung Screening Trial Research Team.  Reduced Lung Cancer Mortality with Low Dose Computed Tomographic Screening.  New England Journal of Medicine, volume 365, pages 395-409, August 4, 2011).  This clinical trial took place in 33 medical centers in theUnited States, and is funded by the National Cancer Institute.

To qualify for enrollment, the patients must have a 30 pack-year smoking history.  About seven million people in theUnited Statesare in this category.  For this clinical trial, 53,454 patients were enrolled between 2002 and 2004, and followed until 2009.  The people were randomly assigned to chest CT or chest x-ray performed once yearly for three years.  Lung tumor was discovered in 645 cases per 100,000 person-years in the CT group, in comparison to 572 in the chest x-ray group.  There were 247 lung cancer deaths per 100,000 person-years in the CT group, versus 309 in the chest x-ray group.  This calculates to a 20% reduction in mortality.

           The bad news is that 96.4% of the abnormal chest CT findings turned out to be benign, meaning false positives.  In other words, an abnormality on the CT translates into a cancer diagnosis in only 3.6% of the time.  This means that many of these patients had more radiological tests done, tests that are in retrospect "unnecessary".  Some people underwent needle biopsies, bronchoscopy and/or chest surgeries in order to determine whether they have a lung tumor or not.  Some of these cases resulted in complications (and even deaths), as expected of invasive procedures in the chest.  The group that underwent screening with chest x-rays also experienced the same problem, as 94.5% of the abnormal chest x-ray findings also turned out to be benign.

           Due to this high level of false positives, chest CT is currently not yet widely recommended for routine screening for lung cancer in the asymptomatic population at large.  Certainly, if you are a current or past smoker and you have any chest symptoms (cough, pain, shortness of breath, hoarseness, wheezing, fatigue, weight loss, etc.), then you should go see a health care professional, who may determine that workup with chest x-ray and chest CT is warranted.