Who should get lung cancer screening?

Adults aged 50 to 80 with a 20 pack-year smoking history who currently smoke or quit within the past 15 years. The US Preventive Services Task Force recommends "annual screening for lung cancer with low-dose computed tomography (LDCT)" for that group, and gives it a grade B.

All four parts of that sentence carry weight, so it is worth taking them one at a time.

A pack-year is one pack a day for one year. Twenty pack-years could mean a pack a day for 20 years, or two packs a day for 10 years, or half a pack a day for 40 years. Work yours out before the appointment. People routinely underestimate it.

The 15-year rule is about quitting, not about age. Risk falls after you stop, and after 15 smoke-free years the balance of benefit and harm shifts.

Where these numbers come from

They are not arbitrary. They come from a trial. The National Cancer Institute reports that in the National Lung Screening Trial, "three annual low-dose CT screens for lung cancer reduced lung-cancer mortality by 20%."

That is a large effect for a screening test, and it is why the criteria are drawn tightly around the group studied. Screening people at much lower risk means running the harms without the same benefit.

The rule most people never hear

USPSTF also says when to stop. "Screening should be discontinued once a person has not smoked for 15 years or develops a health problem that substantially limits life expectancy or the ability or willingness to have curative lung surgery."

Read that last clause again. Screening is only worth doing if a finding would lead somewhere. If someone would not be well enough for lung surgery, or would not want it, a scan cannot help them and can still cause worry, biopsies, and radiation.

The costs of screening, in numbers

A low-dose CT is not free of downside. NCI puts the radiation dose at "1.5 mSv," which it compares to about six months of natural background radiation. Small, but not zero, and this is an annual test.

False alarms are the bigger issue. NCI notes that people screened this way "can have false-positive results (that is, findings that appear to be abnormal even though no cancer is present), which need monitoring." Most spots found on a first scan are not cancer. They lead to follow-up scans, and sometimes to a biopsy.

Knowing that in advance takes some of the fear out of the phone call that says something was seen.

If you have never smoked

The criteria are built entirely around smoking history, so people who have never smoked fall outside them. Their risk is generally low enough that screening is unlikely to help, even though lung cancer in never-smokers does happen.

That makes symptoms more important for this group. A cough that will not settle, coughing up blood, shortness of breath, chest pain, or unexplained weight loss deserves a visit, whatever your smoking history.

What to do next

Add up your pack-years, count the years since you quit, and take both numbers to your doctor. If you qualify, screening is annual, not one-time. And if you still smoke, screening does not replace quitting. The two together do far more than either alone.