Demystifying Medicine One Month at a Time


Dear Glass:

I loved your recent piece on unnecessary screening tests in the Atlantic.

“Letters! We’ve got letters!”

You explain things so simply and clearly. Kudos!

One question, though. I understand when you say in general that CT scans for lung cancer screening can be dangerous. Excess radiation exposure, incidentalomas, cost, etc. I get it. But for those occasions when someone gets a lung tumor discovered early, don’t you think the screening is actually worth it? I mean, how can finding cancer earlier NOT prolong life?


Paula from Paducah

Good question. Two related answers.

The first is the concept of lead-time bias. [Look at figure 2 in the article linked here.]

Simply defined, lead-time bias gives a the false impression of prolonged life, because the time of diagnosis occurs earlier. But in diseases for which the treatment we have doesn’t alter the course of the illness (like lung cancer), we do not actually prolong life. So the “early” diagnosis is in fact an artifact.

Reason 2 is that lung cancer discovered on screening CTs is usually too far advanced to make early treatment meaningful in terms of survival benefit. Put another way, even if you know earlier that you have the illness, it doesn’t make a difference (in aggregate) for people with the disease.

This stuff is hard because if you’re the one (or you have a family member or friend) with the disease, it seems logical that it HAS to make a difference to find the information sooner rather than later.

Sadly, at this point, it’s just not true.


  1. Keith Rockey

    How about the literature showing reduced mortality with low dose Ct screening. As a radiologist I can certainly state that current technology does improve detection of early lung cancers over standard chest radiographs and those tumors detected and less than 1 cm have a high cure rate . And soon we will move completely away from chest radiographs and towards only Chest Ct. Radiation dose s being significantly reduced with dose reduction technology and new imaging algorithms . Yes unnecessary studies need to be avoided but you are muddying the waters in your discussion with old facts.

  2. Emeline Lavanchy

    Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue or other parts of the body. Most cancers that start in lung, known as primary lung cancers, are carcinomas that derive from epithelial cells. ….^-

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