Critical Thinking

It seems that some people don't understand the nature and purpose of diagnostic labels. While it is essentially unambiguous that you have, say, a compound fracture of the femur or infection with pathogenic E. coli, many diagnostic labels are a matter of judgment. They do not correspond to definite entities, but rather have a pragmatic function.

Think of the decision by the International Astronomical Union to declare that Pluto is not a planet. There was an outcry, I imagine because people had been taught about the nine planets in school (and there's even a symphony!) and being told that there are only 8 is very discomfiting. But the point is that there are millions of objects in the solar system. People started calling certain objects planets before they knew anything about them, in fact when people thought the whole universe revolves around the earth. The "planets" were stars that appeared to move against the background of the other stars. The name means "wanderer." But only five of them were visible. Once people started looking with telescopes they found Uranus, Neptune and eventually Pluto, then they figured out that earth was the same kind of thing and earth became a planet.

But what about smaller objects? It didn't seem like a big problem because there was such a huge gap between the biggest asteroids and Pluto. But then astronomers realized that there are many objects beyond the orbit of Pluto that are similar to it, and just as big or bigger. They are all mostly ice, unlike the other planets that are either rocky or presumably have rocky cores. (We don't know for sure what's inside the gas giants, but the leading theories of solar system formation presume solid centers.) Also, Pluto is too small to have cleared all the other junk from its orbit. So they decided to change the definition of "planet" to simplify matters. Nothing about Pluto has changed, they just moved the boundaries of the definition of a planet.

It's the same way with many medical diagnoses. In psychiatry this is most apparent, since for psychiatric disorders there aren't any objectively definable physical parameters. So you get lists of symptoms, all of which are established by subjective judgment, and if the person has three from column A and two from column B they get the label. But it's also true for, say, hypertension or diabetes. The definition of hypertension has changed over the years as evidence about levels of blood pressure that are associated with risk has changed. It used to be that 140/90 was considered the threshold, but now doctors want to get it down to 120.

Cancer is kind of like the planets. Before we had microscopes and X-ray machines and DNA tests, cancer was a bunch of  lumps that started growing in or on people. Then it became possible to detect tiny lumps that could not be seen or felt, and to look at cells under the microscope and see that they were abnormal. Physicians started calling these entities "cancer" because they presumed they would develop into malignancy in time. But then they figured out that isn't necessarily true, and we have proposals to stop calling some of these phenomena cancer. Like Pluto, they haven't changed, but our understanding of them has.

So suggesting that physicians not tell patients that certain abnormal cells are cancer is not telling physicians to lie to people. On the contrary, it's finding a way of getting closer to the truth. Science, including medical science, is not static. When ideas change, it doesn't invalidate science. It means we're making progress, that we know more now than we once did. That's a good thing, as Martha Stewart says.