Ask the Doctors

Dear Doctor: I smoked for more than 20 years. And although I stopped about 20 years ago -- I'm now in my early 60s -- I worry about what changes it might have wrought in my cells. Should I get a CT scan just to be sure?

Dear Reader: Your concern is understandable. Tobacco smoke is a potent carcinogen, and lung cancer is the leading cause of cancer death among both men and women in the United States. On the plus side, detection of budding lung cancers saves lives. Among people diagnosed with Stage 1 lung cancer, the survival rate is 92 percent at five years; the survival rate for those with Stage 4 lung cancer is 6 to 8 percent.

As for whether CT scan screening specifically can reduce deaths from lung cancer, let's look at the numbers. A 2011 study analyzed data of 53,454 men and women who had a 30 pack-year or greater smoking history; a 30 pack-year is the equivalent of smoking one pack of cigarettes daily for 30 years. The participants were either current smokers or had stopped within the last 15 years. The study compared the results of having either yearly CT scans or yearly X-rays for three years, and the participants were followed on average for just over six years.

Screening X-rays had no real benefit in reducing the lung cancer death rate, but CT screening did -- a 20 percent reduction, in fact. That's because CT scans were much more likely to find cancers. Previous trials of CT screening had not shown the same survival benefits because those trials were much smaller.

CT screening for lung cancer is not without risk. For starters, CT scans detect many nodules that are not cancer. This can lead to additional scans to evaluate the nodule or to a biopsy of the lesion, potentially requiring major surgery. In the 2011 study, 96 percent of nodules 4 millimeters or greater -- considered a positive finding in this trial -- were not lung cancer. Nonetheless, invasive procedures were needed to address 11 percent of those nodules, creating the associated risks of lung collapse, bleeding and death.

Also, the chest radiation incurred through such scans could potentially increase the risk of radiation-induced cancers. (This concern is somewhat tempered by the use of low-dose CT scans for screening.) Finally, some slow-growing lung cancers found by CT screenings may never have led to a problem.

That said, CT screening for lung cancer does improve overall mortality rates as well as mortality rates from lung cancer. But strict guidelines -- based on the 2011 study -- address who can be screened as part of their insurance coverage. The U.S. Preventive Services Task Force, the American Association for Thoracic Surgery and the American College of Chest Physicians recommend CT screening for those adults ages 55 to 79 who have a 30-pack year history of smoking and who are either current smokers or smokers who have stopped in the last 15 years. Medicare and other insurers follow these guidelines as well.

That's not to say you aren't at risk for lung cancer, but the benefits of lung cancer screening may not be greater than the risks.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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