As a result of mammography, the number of non-invasive breast cancers diagnosed has risen dramatically in the past decade. But in many cases these early tumors are being overtreated, according to a study to be published today in the Journal of the American Medical Association.
The incidence of ductal carcinoma in situ, or DCIS early cancers or precancers within the milk ducts - has risen 200 percent over 10 years, said researchers from the University of California, San Francisco. Before 1983, when mammography was less common, DCIS accounted for only 0.3 percent of breast cancers diagnosed. Now it accounts for more than 12 percent of breast cancers overall and from 30 percent to 40 percent of those detected by mammograms.
“Are we doing women a favor in detecting these precancerous lesions or not? Are we picking up breast cancer and benefiting them? Or are we picking up lesions that are technically abnormal but may never progress to invade the breast?” asked the lead researcher, Dr. Virginia Ernster.
The study is the first major look at who gets these tumors and how they are treated, said Dr. Mark Citron, head of medical oncology at Long Island Jewish Medical Center in New Hyde Park, N.Y. It is important, he said, because it will help point the way toward figuring out which ones to treat and how aggressively.
Lack of knowledge has been a problem in deciding how to treat DCIS, experts say. “Mammography gave us the ability to find DCIS lesions, and as a result … we didn’t know quite what to do with (them), ” said Dr. Roy Jensen of Vanderbilt University in Nashville, Tenn. Jensen and Dr. David Page say in an accompanying editorial that DCIS is an umbrella term for several kinds of tumors, some of which may develop into invasive breast cancer and some of which may remain in the ducts and cause no damage.
Nonetheless, the researchers found that about 44 percent of such tumors are still treated by mastectomy. By contrast, many invasive, potentially lethal cancers are routinely treated by lumpectomy, a more limited surgery, plus radiation.