What the Dog Saw [90]
According to Donald Berry, who is the chairman of the Department of Biostatistics and Applied Mathematics at M. D. Anderson Cancer Center, in Houston, a woman’s risk of death increases only by about 10 percent for every additional centimeter in tumor length. “Suppose there is a tumor size above which the tumor is lethal, and below which it’s not,” Berry says. “The problem is that the threshold varies. When we find a tumor, we don’t know whether it has metastasized already. And we don’t know whether it’s tumor size that drives the metastatic process or whether all you need is a few million cells to start sloughing off to other parts of the body. We do observe that it’s worse to have a bigger tumor. But not amazingly worse. The relationship is not as great as you’d think.”
In a recent genetic analysis of breast-cancer tumors, scientists selected women with breast cancer who had been followed for many years, and divided them into two groups — those whose cancer had gone into remission, and those whose cancer had spread to the rest of their body. Then the scientists went back to the earliest moment that each cancer became apparent and analyzed thousands of genes in order to determine whether it was possible to predict, at that moment, who was going to do well and who wasn’t. Early detection presumes that it isn’t possible to make that prediction: a tumor is removed before it becomes truly dangerous. But scientists discovered that even with tumors in the one-centimeter range — the range in which cancer is first picked up by a mammogram — the fate of the cancer seems already to have been set. “What we found is that there is biology that you can glean from the tumor, at the time you take it out, that is strongly predictive of whether or not it will go on to metastasize,” Stephen Friend, a member of the gene-expression team at Merck, says. “We like to think of a small tumor as an innocent. The reality is that in that innocent lump are a lot of behaviors that spell a potential poor or good prognosis.”
The good news here is that it might eventually be possible to screen breast cancers on a genetic level, using other kinds of tests — even blood tests — to look for the biological traces of those genes. This might also help with the chronic problem of overtreatment in breast cancer. If we can single out that small percentage of women whose tumors will metastasize, we can spare the rest the usual regimen of surgery, radiation, and chemotherapy. Gene-signature research is one of a number of reasons that many scientists are optimistic about the fight against breast cancer. But it is an advance that has nothing to do with taking more pictures, or taking better pictures. It has to do with going beyond the picture.
Under the circumstances, it is not hard to understand why mammography draws so much controversy. The picture promises certainty, and it cannot deliver on that promise. Even after forty years of research, there remains widespread disagreement over how much benefit women in the critical fifty-to-sixty-nine age bracket receive from breast X-rays, and further disagreement about whether there is enough evidence to justify regular mammography in women under fifty and over seventy. Is there any way to resolve the disagreement? Donald Berry says that there probably isn’t — that a clinical trial that could definitively answer the question of mammography’s precise benefits would have to be so large (involving more than five hundred thousand women) and so expensive (costing billions of dollars) as to be impractical. The resulting confusion has turned radiologists who do mammograms into one of the chief targets of malpractice litigation. “The problem is that mammographers — radiology groups — do hundreds of thousands of these