Ductal carcinoma in situ of the breast (DCIS) is an early, noninvasive stage of breast malignancy that arises from ductal epithelium and has an especially favorable prognosis. Its biologic characteristics are consistent with a direct precursor to invasive carcinoma, which develops in the majority of cases if left untreated, generally within 10 years of diagnosis. Mammography has resulted in a substantial increase in its diagnosis, as well as a change in its presentation from large, palpable masses to nonpalpable lesions manifested primarily as microcalcifications. The same treatment options are available for DCIS as for invasive breast carcinoma, and there is also a limited role for wide local excision alone in incidental lesions. Most cases of DCIS currently are treated effectively by lumpectomy and radiation therapy, although the fact that 50% of all local breast recurrences are invasive lesions may affect survival adversely. Mastectomy is associated with the best survival rates and should be performed on any patient with factors known to pose a high risk of locoregional recurrence. There are still many outstanding issues to be resolved by further study before the intriguing potential of this disease can be realized fully.

Since the first pathologic studies of breast cancer were undertaken in the nineteenth century, an intraepithelial stage has been recognized in the transition from normal tissue t o invasive cancer. In 1932 this was labeled in situ breast carcinoma, but was rarely diagnosed and considered only a clinical oddity. With the establishment of screening mammography over the past 20 years, both the ductal and lobular types of in situ breast carcinoma have been increasingly diagnosed. The lobular variant, lobular carcinoma in situ (LCIS), is now considered a marker of risk for subsequent invasive cancer, and is managed expectantly without surgical ablation. The ductal form, ductal carcinoma in situ (DCIS), is considered a true premalignant lesion, which should be treated largely in the same way as invasive breast carcinoma. An understanding of the epidemiology and biologic implications of DCIS is necessary for a rational approach to treatment. N Key Words: DCIS, noninvasive breast cancer, in situ breast cancer HISTORICAL PERSPECTIVEost of the original pathologic investigations of M malignant tumors, which took place in the nineteenth century, focused on breast carcinoma. These studies documented that carcinoma arises from normal epithelial cells, and several investigators were able to trace

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