False positives plague lung cancer screening

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DEAR DR. ROACH: I’m a 74-year-old female who smoked a pack a day for 40-plus years, having quit smoking about 18 years ago. As a precaution, I asked my primary doctor to order a screening CT scan, knowing that I’m a candidate for lung cancer. The results showed a 3-mm nodule in one lung, and I was advised not to worry and that my doctor would order another CT scan in six months. I can’t help but wonder if this is cancer and if an oncologist, after six months, will ask me why I waited so long to see him. – T.W.

ANSWER: Medical professionals have been attempting to screen for lung cancer for decades. Chest X-rays proved insensitive: By the time cancer could be seen on X-ray, it was usually too late to do anything about it. CT scans are much more sensitive (maybe too sensitive; see below), and studies have shown that some lives will be saved with a screening program. However, the number of people who would benefit is relatively small; 256 moderate-to-heavy smokers would need yearly screening for three years in order to prevent one lung cancer death.

There are two other significant concerns about lung cancer screening. The first is the issue you have now: an abnormal result and what to do about it. It’s extremely common. Almost 25% of scans will be abnormal, and 96% of the abnormal results will be false positives. But it will require multiple scans and sometimes an invasive procedure to prove it. This means a great deal of anxiety among people who get the type of result you did.

The small size of your nodule means your risk that this nodule is cancer is much lower than 1%. A follow-up scan is the usual recommendation, and if the nodule is the same size or smaller, the chance of it being cancer is very close to zero. You should have had a careful explanation of the likelihood of false positive results before getting the scan. You should also have been warned of the possible need for a biopsy and the possible financial costs associated with follow-up testing.

The second concern is that current smokers who consider screening should receive intensive advice and help in quitting smoking. A negative CT scan is not a “clean bill of health” for a smoker and quitting remains the single most important thing most smokers can do for their overall health.

DEAR DR. ROACH: How often does a healthy person with perfect vision and no eye concerns need to see an eye doctor? – D.S.

ANSWER: A periodic eye exam in someone with no symptoms involves a screening test for vision changes related to aging and other eye diseases, including glaucoma, age-related macular degeneration and cataracts. There are several commonsense reasons for screening, but there has not been good evidence to support its use.

The U.S. Preventive Services Task Force does not make a recommendation for or against screening. The Canadian Task Force recommends against it. By contrast, the American Academy of Ophthalmologists recommends a baseline exam at age 40; visits every two to four years from age 40-54; every year to three years from age 55-64; and annual exams for people 65 and over.

Dr. Roach regrets he is unable to answer individual letters, but he will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu.

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