False positive rate plagues screening

Dear Dr. Roach: I’m a 74-year-old female who smoked a pack a day for 40-plus years, having quit smoking about18 years ago. 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. I can’t help but wonder if this is cancer and if an oncologist will ask me why I waited so long to see him. — T.W.

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, and studies have shown that some lives will be saved with a screening program. However, the number of people who would benefit is small.

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.

The small size of your nodule means your risk that this nodule is cancer is much lower than1%. 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. You should also have been warned of the possible need for a biopsy and the possible costs.

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.