An update on screening for lung cancer

Sophisticated computed tomography (CT) scanning can detect lung tumors early. But the question remains unanswered whether using it to screen people at risk for lung cancer will save lives. Could it even do more harm than good?

Lung cancer is one of the deadliest forms of cancer for both men and women. It accounts for more
deaths than cancers of the breast, prostate gland, colon, and pancreas combined. That fact has
been a driving force in the search for a screening test that, like mammography for breast cancer, could detect tumors at an early stage, when they may be more curable. Typically, by the time people have symptoms and are diagnosed, the cancer has spread beyond the lungs, and the
chance of successful treatment is greatly reduced.

Unfortunately, evidence that screening saves lives has been controversial. Even use of sophisticated CT scans to test people at increased cancer risk has not changed the situation.

Looking at the research

To get a definitive answer about the usefulness of CT screening, many doctors have been awaiting the results of the National Lung Screening Trial (NLST), a large-scale controlled study sponsored by the National Cancer Institute. The trial, focused on smokers and former smokers, is comparing 2 screening methods—standard chest x-rays and spiral CT, which can detect even tiny tumors.

One study gives hope

Then this past fall, a study was reported that seemed to weigh heavily in favor of CT screening. It suggested that not only can CT detect lung tumors early but that if these tumors are treated, survival can be greatly extended.

The study team screened more than 31,000 people who had no symptoms of lung cancer but were at increased risk for the disease because of their history of cigarette smoking or exposure to occupational chemicals, asbestos, or secondhand smoke. Over 12 years, 484 people were diagnosed with lung cancer—more than 80% with stage I disease, the earliest stage and the only one for which a surgical cure is likely. The researchers estimated the 10-year lung cancer survival rate among the study’s 484 lung cancer patients
to be 80%—regardless of the stage of their cancer or how they were treated. Among those with stage I lung cancer, the cure rate would be 88%.

Other recent research involving smokers and former smokers who were screened using CT came up with similar findings. But it led the investigators to a very different conclusion about the value of screening. CT detected many small tumors; however, advanced cancers were numerous as well among those screened. Moreover, some small tumors never become dangerous. Thus, noted experts, what may look like an opportunity to extend survival may, in fact, be an unnecessary diagnosis leading to unnecessary surgery.

More harm than good?

That raises the issue of the trade-off between benefit and harm when considering whether to recommend lung cancer screening using current methods. Detection of even small tumors may trigger follow-up involving further, diagnostic scanning and needle or surgical biopsy (removal of a sample of tissue for lab examination). And if surgery is indicated, it carries up to a 5% risk of death and a 20% risk of serious complications. In the future, researchers believe, a combination of CT and tests for cancer markers may make it possible to identify early tumors that truly require treatment.

From The New England Journal of Medicine, The Journal of the American Medical Association, and the National Cancer Institute