As the use of screening mammography has increased, the detection of DCIS--which usually cannot be felt by a clinical exam--has also risen. But because the lesions are removed when detected, doctors are uncertain what percentage of such lesions, if untreated, would progress to invasive breast cancer. Studies have shown that only a fraction of women with DCIS treated by lumpectomy (removal of the lump) alone later progress to invasive cancer. Thus, there is a concern that diagnosis and treatment of many DCIS cases may not be beneficial.
To determine the frequency of DCIS detection in screening mammography, Virginia L. Ernster, Ph.D., of the University of California, San Francisco, and Rachel Ballard-Barbash, M.D., of the National Cancer Institute, and their colleagues linked mammography data from 540,738 women between the ages of 40 and 84 to population-based cancer and pathology registries. The authors then calculated the percentage of screen-detected breast cancers that were DCIS and the rate of DCIS per 1000 mammograms.
They found that approximately 20% of the breast cancers detected by screening mammography were DCIS and that the overall rate of DCIS detected by mammography was approximately 1 in every 1,300 mammograms. They also found that the percentage of screen-detected breast cancers that were DCIS decreased with age. For example, in women aged 40 to 49, 28.2% of screen-detected breast cancers were DCIS whereas in women aged 70 to 84, 16% of screen-detected breast cancers were DCIS. However, the rate of DCIS diagnoses per 1000 mammograms increased with age, from 0.56 per 1000 for women ages 40 to 49 to 1.07 per 1000 for women ages 70 to 84. Further analysis revealed that mammograms were more sensitive at detecting DCIS than they were for detecting invasive breast cancer.
The authors point out that the likelihood of benefit from treatment of DCIS is probably greater for women with larger, higher grade lesions than for those with very small, low-grade lesions. "Given the uncertainty about the natural history of DCIS, the clinical significance of screen-detected DCIS needs further investigation," the authors conclude.
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Ernster V, Ballard-Barbash R, Barlow W, Zheng Y, Weaver D, Cutter G, et al. Detection of ductal carcinoma in situ in women undergoing screening. J Natl Cancer Inst 2002;94:1546-54.
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