Is CT screening for lung cancer a good idea?

Lots of media coverage would say that it is: the Independent puts it:

“Screening heavy smokers with low-dose computer tomography (CT) instead of X-rays can reduce deaths from lung cancer by 20 percent, a massive US study released Thursday shows. Previous studies have shown that helical CT scanning can identify small tumors in the early stages of growth better than X-rays. “But it’s never been shown before conclusively that the procedure has an effect on the ultimate outcome, namely lung cancer mortality,” Harold Varmus, head of the National Cancer Institute, told reporters.”

Well….the screening story regarding lung cancer is an interesting one. I have not been convinced about the evidence for screening up till now, and it is reasonable that a decent trial goes ahead to try and decide if screening people for lung cancer will be beneficial. The study generating the coverage is this one, a RCT comparing chest xray to CT scans in heavy smokers. There are problems, starting with this one – this research hasn’t yet been published in a peer reviewed journal, hence we don’t know all the details. The trial has been stopped early because there was concern that it was becoming clear that CT screening was statistically significantly better for survival. The National Cancer Institute do a good job in explaining the caveats so far; e.g.

“Should all smokers have low-dose helical CT to screen for lung cancer and/or other diseases?
Not necessarily. The NLST participants were a very specific population of men and women ages 55 to 74 who were heavy smokers. They had a smoking history of at least 30 pack-years but no signs or symptoms of lung cancer at the beginning of the trial. Pack-years are calculated by multiplying the average number of packs of cigarettes smoked per day by the number of years a person has smoked. It should also be noted that the population enrolled in this study, while ethnically representative of the high-risk U.S. population of smokers, was a highly motivated and primarily urban group, and these results may not fully translate to other populations. Men and women in a similar age group and with a similar smoking history should be aware that not all lung cancers found with screening will be early stage. … A diagnostic CT is done after a person has a sign or symptom of disease, while a screening CT looks for initial signs of disease in healthy people.”

This is getting to the heart of the matter, and read on for a good explanation of lead time bias. I’m concerned that private screening companies in the UK will use this study as a reason to market CT scans at smokers – we don’t yet have enough information to tell us who is likely to benefit and with what risks attached. And if there is a benefit to this type of screening, we need the full data before we can advise people of the possibly negative outcomes of screening – and what kind of chance there is of lengthening your life because of it. At the moment, despite past ASA restrictions, such companies persist in overselling their products, and I’m afraid this will be yet another opportunity to do the same.

One Response to “Is CT screening for lung cancer a good idea?”

  1. szigetiroland November 9, 2010 at 5:23 pm #

    REDuce mortality s is the key.