What the Dog Saw [84]
2.
The head of breast imaging at Memorial Sloan-Kettering Cancer Center, in New York City, is a physician named David Dershaw, a youthful man in his fifties, who bears a striking resemblance to the actor Kevin Spacey. One morning not long ago, he sat down in his office at the back of the Sloan-Kettering Building and tried to explain how to read a mammogram.
Dershaw began by putting an X-ray on a light box behind his desk. “Cancer shows up as one of two patterns,” he said. “You look for lumps and bumps, and you look for calcium. And, if you find it, you have to make a determination: is it acceptable, or is it a pattern that might be due to cancer?” He pointed at the X-ray. “This woman has cancer. She has these tiny little calcifications. Can you see them? Can you see how small they are?” He took out a magnifying glass and placed it over a series of white flecks; as a cancer grows, it produces calcium deposits. “That’s the stuff we are looking for,” he said.
Then Dershaw added a series of slides to the light box and began to explain all the varieties that those white flecks came in. Some calcium deposits are oval and lucent. “They’re called eggshell calcifications,” Dershaw said. “And they’re basically benign.” Another kind of calcium runs like a railway track on either side of the breast’s many blood vessels — that’s benign, too. “Then there’s calcium that’s thick and heavy and looks like popcorn,” Dershaw went on. “That’s just dead tissue. That’s benign. There’s another calcification that’s little sacs of calcium floating in liquid. It’s called ‘milk of calcium.’ That’s another kind of calcium that’s always benign.” He put a new set of slides against the light. “Then we have calcium that looks like this — irregular. All of these are of different density and different sizes and different configurations. Those are usually benign, but sometimes they are due to cancer. Remember you saw those railway tracks? This is calcium laid down inside a tube as well, but you can see that the outside of the tube is irregular. That’s cancer.” Dershaw’s explanations were beginning to be confusing. “There are certain calcifications in benign tissues that are always benign,” he said. “There are certain kinds that are always associated with cancer. But those are the ends of the spectrum, and the vast amount of calcium is somewhere in the middle. And making that differentiation, between whether the calcium is acceptable or not, is not clear-cut.”
The same is true of lumps. Some lumps are simply benign clumps of cells. You can tell they are benign because the walls of the mass look round and smooth; in a cancer, cells proliferate so wildly that the walls of the tumor tend to be ragged and to intrude into the surrounding tissue. But sometimes benign lumps resemble tumors, and sometimes tumors look a lot like benign lumps. And sometimes you have lots of masses that, taken individually, would be suspicious but are so pervasive that the reasonable conclusion is that this is just how the woman’s breast looks. “If you have a CAT scan of the chest, the heart always looks like the heart, the aorta always looks like the aorta,” Dershaw said. “So when there’s a lump in the middle of that, it’s clearly abnormal. Looking at a mammogram is conceptually different from looking at images elsewhere in the body. Everything else has anatomy — anatomy that essentially looks the same from one person to the next. But we don’t have that kind of standardized information on the breast. The most difficult decision I think anybody needs to make when we’re confronted with a patient is: Is this person normal? And we have to decide that without a pattern that is reasonably stable from individual to individual, and sometimes even without a pattern that is the same from the left side to the right.”
Dershaw was saying that mammography doesn’t fit our normal expectations of pictures. In the days before the invention of photography, for instance, a horse in motion was represented in drawings and paintings according to the convention