What the Dog Saw [89]
In 1987, pathologists in Denmark performed a series of autopsies on women in their forties who had not been known to have breast cancer when they died of other causes. The pathologists looked at an average of 275 samples of breast tissue in each case, and found some evidence of cancer — usually DCIS — in nearly 40 percent of the women. Since breast cancer accounts for less than 4 percent of female deaths, clearly the overwhelming majority of these women, had they lived longer, would never have died of breast cancer. “To me, that indicates that these kinds of genetic changes happen really frequently, and that they can happen without having an impact on women’s health,” Karla Kerlikowske, a breast-cancer expert at the University of California at San Francisco, says. “The body has this whole mechanism to repair things, and maybe that’s what happened with these tumors.” Gilbert Welch, the medical-outcomes expert, thinks that we fail to understand the hit-or-miss nature of cancerous growth, and assume it to be a process that, in the absence of intervention, will eventually kill us. “A pathologist from the International Agency for Research on Cancer once told me that the biggest mistake we ever made was attaching the word ‘carcinoma’ to DCIS,” Welch says. “The minute carcinoma got linked to it, it all of a sudden drove doctors to recommend therapy, because what was implied was that this was a lesion that would inexorably progress to invasive cancer. But we know that that’s not always the case.”
In some percentage of cases, however, DCIS does progress to something more serious. Some studies suggest that this happens very infrequently. Others suggest that it happens frequently enough to be of major concern. There is no definitive answer, and it’s all but impossible to tell, simply by looking at a mammogram, whether a given DCIS tumor is among those lesions that will grow out from the duct, or part of the majority that will never amount to anything. That’s why some doctors feel that we have no choice but to treat every DCIS as life-threatening, and in 30 percent of cases that means a mastectomy, and in another 35 percent it means a lumpectomy and radiation. Would taking a better picture solve the problem? Not really, because the problem is that we don’t know for sure what we’re seeing, and as pictures have become better we have put ourselves in a position where we see more and more things that we don’t know how to interpret. When it comes to DCIS, the mammogram delivers information without true understanding. “Almost half a million women have been diagnosed and treated for DCIS since the early nineteen-eighties — a diagnosis virtually unknown before then,” Welch writes in his new book, Should I Be Tested for Cancer?, a brilliant account of the statistical and medical uncertainties surrounding cancer screening. “This increase is the direct result of looking harder — in this case with ‘better’ mammography equipment. But I think you can see why it is a diagnosis that some women might reasonably prefer not to know about.”
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The disturbing thing about DCIS, of course, is that our approach to this tumor seems like a textbook example of how the battle against cancer is supposed to work. Use a powerful camera. Take a detailed picture. Spot the tumor as early as possible. Treat it immediately and