Ductal carcinoma in situ (DCIS) is a very early form of breast cancer confined to the milk ducts. Before the advent of mammography, DCIS was difficult to detect and was often missed entirely or diagnosed as benign. Now, it's more easily found and makes up a growing percentage of breast cancer cases. The good news is that the disease is at such an early stage (many experts even describe the condition as pre-cancerous) that most women can be successfully treated. The bad correlate, however, is that only about half of all DCIS progresses to invasive cancer, which means many women undergo unnecessary treatment. Researchers know now that DCIS ranges in aggressiveness from low to high. Women with big lesions of high-grade DCIS usually are treated with mastectomy to prevent invasive cancer. But less is known about what happens to small lesions of low-grade DCIS if they are left untreated.

What the researchers wanted to know: What happens to low-grade DCIS if left alone and not treated?

What they did: Researchers at the Vanderbilt University Medical Center in Nashville followed a group of 28 women who, between 1950 and 1968, were diagnosed with what doctors then thought were benign breast lesions. They had breast biopsies but were not otherwise treated. As diagnostic criteria evolved over the years, these lumps were retrospectively reclassified as low-grade DCIS. Researchers have been following up with these women to see what happened to them‑whether any of them later developed invasive breast cancer. They've already reported on their status twice, and are now are back to see if, even 40 years after the initial biopsy, there is still an additional risk of developing invasive cancer.

What they found: Even low grade DCIS poses a significant risk of developing into invasive breast cancer. After 46 years, 11 of the 28 women–40 percent–had developed invasive cancer, all of them in the same breast and area of the breast as the original DCIS lesion. Most of the women saw an invasive cancer appear during the first 15 years after diagnosis, but three were diagnosed between 23 and 42 years after their original biopsy. Five developed metastatic disease–one as late as 29 years after her biopsy‑and died within 7 years of that diagnosis. The bottom line, the authors say, is that there's a 30 percent chance of developing invasive breast cancer in the 15 years after low-grade DCIS is found.

What the study means to you: The study provides support for the treatment of even low-grade DCIS. But the authors say that these small, low-grade lesions can usually be treated simply by removing them surgically. A full-blown mastectomy or a lumpectomy plus radiation treatment probably amounts to overtreatment in these cases. The study also distinguished between DCIS and a less serious form of tissue abnormality, atypical ductal hyperplasia, which carries about half the risk of progressing to invasive cancer. The decision about how to treat DCIS depends on the accurate diagnosis of the disease, the authors say–so it is critically important that the grade of DCIS is correctly identified. If low-grade DCIS isn't fully removed, it may eventually progress.

Caveats: The study is of only 28 women, but larger studies aren't likely to be conducted because it would be unethical to not treat women with DCIS simply to find out how the disease progresses. The findings are similar to a previous study, and as the authors say, likely represent the only information that will be available on what happens to low-grade DCIS when it's untreated.

Find out more: Read information about breast cancer at www.nationalbreastcancer.org.

Read the article: Sanders, M.E. et al. "The Natural History of Low-Grade Ductal Carcinoma in Situ of the Breast in Women Treated by Biopsy Only Revealed Over 30 Years Long-Term Follow-Up." CANCER, Published Online: May 9, 2005 (DOI:10.1002/cncr.21069); Print Issue Date: June 15, 2005.

Abstract online: http://www3.interscience.wiley.com