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Before peering any further into the future, however, it helps to know a little biology. Most breast cancers begin in the milk ducts, narrow passageways that radiate throughout the breast. A few cells, for reasons that are not completely understood, start accumulating genetic mistakes that cause them to grow abnormally. Eventually the cells develop into DCIS. The good thing about DCIS cells is that they haven't spread beyond the milk duct. The bad thing is that they are malignant. "Some people call DCIS precancer, but it's not precancer," says Dr. Dennis Slamon, director of breast-cancer research at the UCLA School of Medicine. "It's preinvasive. It's cancer that hasn't invaded outside the breast ducts."
After a tumor starts to break out of its milk duct, it's often still quite small. About the smallest tumor a mammogram can pick up is 0.5 cm to 1 cm in diameter. By contrast, the average cancers that are felt either by women or their physicians are around 2.5 cm. Even though mammograms still miss about 10% of all tumors, it's their ability to spot smaller tumors, which are generally easier to treat, that keeps women coming back for their annual appointment.
Once the cancer puts down roots in the lymph nodes, the prognosis gets worse. The lymph nodes act as a kind of sewer system for many types of toxins and wastes. Tumors growing in the lymph nodes have a greater chance of breaking off and traveling to the bones, brain, lungs or other parts of the body, where they can seed new growths, called metastases. Here again, doctors used to think that any breast cancer that had spread to the lymph nodes must have been growing a long time. Now they realize that the fact the cancer has shown up in the lymph nodes may have more to do with how aggressive it was from the start than with how long it has been growing.
That's what makes DCIS treatment so controversial. What if most of the tiny tumors that show up in high-resolution mammograms are the ones that grow the slowest or maybe even disappear of their own accord? It probably doesn't matter too much how quickly you treat these slow-growing tumors; most women would survive. And if that's the case, wouldn't it make sense to leave those tumors alone until you could figure out whether they are going to grow? Some breast-cancer experts even speculate that more women may die with these tumors in their breast than because of them.
An intriguing study on invasive tumors, begun in 1988, provides some clues. The trial included about 1,200 women whose tumors were less than 2 cm across with no evidence of malignancy in their lymph nodes and whose cancer cells looked, under the microscope, as if they weren't particularly dangerous. Although these women did not receive the "watchful waiting" approach pioneered in prostate-cancer patients, they weren't treated as aggressively as they might have been. For five years after their tumors were surgically removed, doctors did nothing more unless there was a recurrence. Though 11% of the women did in fact develop a second cancer, their survival rate (and this is the key) was comparable to that of another group of women who had undergone chemotherapy (with or without the drug tamoxifen) at the time of their surgery.
No one is recommending a wholesale "cut and wait" approach for breast cancer—particularly on the basis of a single study. For one thing, waiting to see how aggressive a cancer truly is makes a lot more sense for men in their 80s than for women in their 40s.
The question about what to do with DCIS is also rife with extenuating factors. If DCIS never left the breast ducts, physicians could safely ignore it. No one knows for sure, but at least one study suggests that perhaps 40% of DCIS lesions will develop into invasive tumors that, if left untreated, could eventually prove fatal. That means that maybe 60% of DCIS cases never threaten a woman's health—and therefore these growths do not need to be removed.
Before the routine use of mammograms, most cases of DCIS were discovered accidentally, often during other surgeries. Thanks to better screening, the absolute number of DCIS cases has jumped seven-fold in the U.S. over the past three decades. "At the moment, we don't know which women diagnosed with DCIS might be able to get by with minimal treatment," says Dr. Eric Winer, director of breast oncology at the Dana-Farber Cancer Institute in Boston. As a result, most doctors agree that it's prudent to treat all DCIS cases as if they are dangerous. (In the past couple of years, however, some surgeons have started treating the tiniest, least aggressive DCIS lesions by excision alone, forgoing radiation, provided they can get wide, cancer-free margins around the tumor.)