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The epithelium of the breast ductal system is the site of origin for nearly all breast cancers.1,2 The intraductal environment and the significance of the secretions produced within the human mammary gland have been debated for centuries. The recognition of the role of carcinogens in the production of malignancies led to a renewed interest in the ductal anatomy and physiology in the 20th century. Today, the combination of technological enhancement providing direct and indirect access to the luminal milieu and advances in cellular methodology that hold the promise of reliable diagnostic and predictive markers of breast cancer are driving investigators to pursue a ductal approach to breast cancer diagnosis and therapy that will be preemptive and accurate with less toxicity and breast disfigurement.

The identification of high-risk individuals through statistical screening (ie, Gail and Claus models), histologic or cytologic identification of proliferative breast lesions (ie, atypical ductal or lobular hyperplasia and lobular carcinoma in situ), and recognition of genetic abnormalities (ie, BRCA1 and BRCA2) have resulted in an established paradigm for the management of high-risk individuals. Increased surveillance, chemoprevention, and breast extirpation are designed to either diagnose the disease at a treatable stage or prevent it entirely. If a malignancy is diagnosed, then a multidisciplinary approach, using some combination of local therapy with surgical intervention and radiation therapy and systemic therapy with cytotoxic chemotherapy, hormonal therapy, or targeted therapy is today's standard. Despite dramatic advances, local therapy often results in alterations in the appearance of the breast, and the adverse events associated with systemic therapy remain discouraging.

In defining an ideal intraductal therapy, one seeks an approach that addresses all the tissue at risk, the mammary duct epithelium. Second, the technique for ductal access must be reliable and reproducible, for therapy as well as follow-up. Finally, the agents used intraluminally must exert their effect at a local level without systemic side effects or impact on the consistency or appearance of the breast. This is the challenge facing intraductal investigators. In this chapter, we review recent literature related to the breast ductal anatomy, the preclinical trials evaluating the efficacy of intraducal therapy, and the results of early clinical trials evaluating intraductal therapy.

The anatomy of the breast ductal system has been the subject of much debate. At issue are questions regarding the number of ductal orifices on the surface of the nipple and the distribution of the arborizing ductal network. The literature divides into those that note 15 to 20 ducts and those that report 6 to 9. This discrepancy can be explained in part by the technique used for the study. Those reports that based their observation on cannulating intact nipples or imaging intact lactating or nonlactating breasts all report 6 to 9 functional ductal orifices.3-7 On the other hand, the studies that transected the nipple and described the ductal cross-sections concur on 15 to 20 ducts in the subareolar location.8-11 It is ...

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