Dr. Gerard Silvestri, Medical University of South Carolina, discusses the use of PET scans in lung cancer workup.
You may be asked when you’re diagnosed with lung cancer to have something called a PET scan. Unlike a CT scan, a PET scan tells us not where it is, but is it active — so a PET scan works on this idea that if it “lights up,” it’s an active lesion. Now things that are active tend to be rapidly dividing cells, and so PET is actually not useful in the brain where we are thinking all the time, we have very rapid metabolism. If a lesion lights up in the lung it’s rapidly dividing cells and it may be cancer, although sometimes infections in the lung can cause the PET scan to light up and even changes after radiation treatments can cause a PET scan to “light up.”
The PET scan can tell us if and where lesions are active, and they sometimes pick up disease we didn't suspect outside the chest, for example in the bone, or the adrenal gland, or the liver, so the PET scan is useful if it’s positive and it tells us that a lesion is active. It’s also incredibly useful if it’s negative — so sometimes we have benign spots in our lung and if the PET scan is negative in that area it means, by and large, it’s not cancer.
One strong recommendation in this area though is if you have a positive PET scan it doesn’t always mean cancer; 20% of the time it’s falsely positive, especially in patients that have infections around a certain area. We often recommend doing a biopsy to confirm that the PET scan is in fact really cancer, or could it be something else. Sometimes we’re really surprised at the results of the biopsy in patients who have a positive PET scan and it turned out not to be cancer, which is good news for our patients.