Doctor’s Note: Clearing the Air About Lung Cancer Screening

Lung cancer is the deadliest cancer in the U.S. and worldwide, killing more than 130,000 Americans each year. One reason why is that lung cancers often aren’t caught until it’s too late. As of 2021, only 29 percent of lung cancers were diagnosed at a localized stage. The remaining 71 percent had already spread to lymph nodes or other organs. Most of us have a friend or relative who went to the doctor with a cough or weight loss, only to find out that they had a widespread lung cancer. Sadly, it’s an all-too-common way for the disease to be discovered. And while the treatment and prognosis of lung cancer has made great strides in recent years, it still has much worse long-term survival than colorectal, breast, or prostate cancer.

Doctors have spent great effort over the past century trying to devise a technique for early detection. As early as 1960, people were running clinical trials of regular chest X-ray (CXR) screening. Between 1960 and 2009, hundreds of thousands of patients were enrolled across multiple studies all around the world. Every study showed no benefit to CXR screening. Why did chest X-rays fail? Well, lung cancers just don’t show up very well on conventional X-ray images. By the time they’re visible on plain film, it’s often too late to count as “early detection.”

Low-dose computed tomography (LDCT) is a much newer imaging modality. The first chest LDCT trials were published in 1996, a full century after conventional X-rays. Compared to CXR, CT imaging has far better resolution and the ability to reconstruct 3D slices. This makes it an overwhelmingly superior technology for lung cancer diagnosis, and the clinical trials have borne this out.

In 2011, U.S. investigators published the landmark National Lung Screening Trial study. 53,454 U.S. patients at high risk of lung cancer were randomly assigned to LDCT or CXR screening, and the LDCT group had a 20 percent lower risk of lung cancer death. LDCT imaging greatly increased the early detection rate, with lung cancers diagnosed at Stage I (the earliest stage, where the cancer is still localized) in 31.1 percent of patients screened with X-rays, versus 50.0 percent of LDCT-screened patients. This was the first time anyone had measured a survival advantage for lung cancer screening, but it wouldn’t be the last.

In 2020, Dutch investigators published the NELSON study, with a total of 15,792 participants. Just like the NLST, this trial showed a 24 percent reduced risk of lung cancer death with CT screening. Stage I diagnosis rates increased from 13.5 percent without LDCT screening to 40.4 percent with LDCT screening.

In response to these two positive trials, U.S. clinical guidelines have embraced LDCT lung cancer screening for all patients “at high risk of lung cancer.” This means anyone between the ages of 50-80 with a lifetime smoking history of at least 20 pack-years (a pack-year is the equivalent of smoking 20 cigarettes a day for one year), and is either still smoking or quit less than 15 years ago. The U.S. Preventative Services Task Force has recommended LDCT lung screening with a “B” evidence grade, the same level-of-evidence as mammograms for breast cancer. Just like with breast cancer, screening imaging can’t prevent all cancer deaths, but it does significantly improve your odds.

Unfortunately, the uptake of LDCT lung screening has been far slower than expected. As of 2022, fewer than 1 in 5 eligible Americans reported getting an annual LDCT scan. Unlike mammograms and colonoscopies, most people don’t even know that LDCT exists. Why is that?

Well, LDCT hasn’t been around long enough to make a big impression on the popular consciousness. Compared to chest X-rays (invented 1895), Pap smears (1928), mammograms (1965), and colonoscopies (1969), the LDCT is a newcomer invented in 1993. LDCT technique and interpretation wasn’t fully standardized until the publication of Lung-RADS (the Lung CT Screening Reporting and Data System) in 2014.

You’ve probably been lectured about mammograms and colonoscopies at some point in your life. You may have heard an HR officer describing them as part of your employee benefits, or watched presidential candidates mention them on the campaign trail or debate stage. In contrast, LDCT is too new to be a common topic of discussion. Give it a few years and it may well get there.

One common talking point used to argue against lung cancer screening is that it has a “high false positive rate,” often quoting the “96.4 percent” false positive rate in the 2011 NLST report. All this means is that the overwhelming majority of abnormal findings on LDCT are not lung cancer – they are “false” from a lung cancer detection standpoint. But that’s vastly underselling the utility of LDCT. If you’re diagnosed with emphysema, pneumonia, aortic aneurysm, calcified coronary plaques, or hiatal hernia based on a chest LDCT, it’s a true result that could make a difference to your health. It’s only “false” in the sense of “not a lung cancer.”

If you are an American at high risk of lung cancer due to age and smoking history, it’s likely that you already qualify for annual LDCT screening at little or no out-of-pocket cost. If you have other risk factors for lung cancer, such as an occupational exposure to inhaled chemicals or particles, or a strong family history, then you could qualify for LDCT screening on a case-by-case basis. In either case I strongly recommend that you talk to your primary care doctor about LDCT screening. Lung cancer screening is a proven technology that saves lives.