Hey Doc, Can I Get A Scan Of My Whole Body?

One of the frustrations of practicing medicine (and being a patient) is the huge amount of uncertainty. Unlike engineering, there are very few solid answers when we ask questions of our bodies. What does this particular lab test mean? Well, it depends on the context. What’s the age of the patient? What’s their sex? What are their risk factors?

Many of you have had “callbacks” after a mammogram, a scary experience. The reason we have these callbacks is that the pictures don’t always give us the answers we want. As a patient, I want to know: do I or do I not have cancer. Screening tests like mammograms sometimes give very good, clean answers but often enough they don’t. An abnormal mammogram in a healthy 35 year old is different from one in a 70 year old with a strong family history of breast cancer, even if the xrays look about the same.

Every test we run in medicine is dependent on the context, and there are often complex mathematics that help us determine the difference between two similar results in two different patients. This is one of our biggest challenges, especially in screening tests for cancers. Does an elevated PSA mean you have prostate cancer? Maybe. Depends. Ugh.

The image above is from a CT scan. Picture the patient lying on their back with their feet toward you, then David Copperfield saws them in half through their chest. Like the magic trick, the patient walks away unharmed but we get this great picture. The left side of the picture is the right side of the body, and the arrow is pointing to a lung nodule.

Is it cancer? That depends. Obviously we can tell if we just stick a needle in it or cut it out, but can we get answers without cutting the patient open? Yes-ish.

First we need to know something about the patient: how old are they? Are they a smoker? Do they have a cough? Fevers? Weight loss? Where do they live?

We need to know about the nodule itself. How big is it? Is it solid? Cystic? Cloudy? Are there any earlier films to compare it to?

If this CT scan is from a 65 year old smoker with a cough and unexplained weight loss, and it’s about half a centimeter in diameter (it’s actually about twice that in this pic, but let’s pretend), it’s going to need some close observation or even a biopsy.

If the scan is of a healthy 25 year old who happened to get a CT scan for, say, a car accident, well, we can, at 5mm, safely ignore it. Maybe. But whether or not it is “likely” benign isn’t going to make her feel any better. It will cause anxiety and may lead to unnecessary radiation exposure or an unnecessary biopsy. The biopsy could be complicated by a punctured lung. An otherwise-healthy 25 year old now has some big problems.

If someone comes to me and says, “Doc, can we just get a CT scan of my whole body to see if there’s any cancer?” the safe answer is, “No, that’s not a thing. But here’s what we can do for cancer screening.” We target our cancer screening tests to increase the likelihood of finding a cancer if it’s there, and to decrease the chances of putting someone through a lot of worry and unnecessary, potentially-harmful procedures.

In the above scary-looking CT scan, the patient had “Valley Fever”, a relatively common infection in the Southwest US and California’s Central Valley. Context matters. A lot.

A good primary care doctor can help guide you in making decisions about cancer screening. It can be frustrating as a patient, but it’s far safer than just poking around until you happen to find something.

Stay well.

-pal