Management of atypical breast lesions continues to evolve. There is considerable controversy as to whether these entities represent risk factors for future breast cancer or whether they are instead precursor lesions. A better understanding of the prognostic and therapeutic implications of each of these lesions is important for assessing subsequent breast cancer risk. Risk assessment tools are available for screening high risk patients and understanding the utility and limitations of these tools is important for all clinicians involved in the care of patients. There have been significant advances in breast cancer screening in the last several year including breast tomosynthesis, automated breast ultrasound, molecular imaging, as well as accelerated breast MRI protocols. This has raised the question: Do women at risk for breast cancer need additional breast cancer screening using these newer imaging modalities? In addition, with these advances in imaging, can women with atypical proliferative lesions be observed rather than undergoing surgical excision as some suggest? The role of observation, surgical excision and even prophylactic mastectomy in women with atypical proliferative lesions continues to be debated; however there is data that can guide physicians in the management of these patients. Pleomorphic Lobular carcinoma in-situ (PLCIS) is a distinct pathological entity within LCIS and there is no consensus regarding surgical margins or the need for adjuvant treatment to prevent recurrence. Recently, ductal carcinoma in-situ (DCIS) has been the subject of much controversy: is it truly a cancer or is it instead a precursor lesion. The traditional management of DCIS with lumpectomy and radiation is now being debated and recent data demonstrates that low grade DCIS can be managed with observation. Clinical trials are now accruing patients with low and intermediate grade DCIS to observation and close surveillance, and not surgical excision. Finally, new guidelines for chemoprevention with the use of tamoxifen and raloxifen for women with atypical proliferative lesions, LCIS, PLCIS, and DCIS are available and should be discussed as an option when guiding management of these patients. This book will provide a comprehensive review of this field and will serve as a valuable resource for clinicians, general surgeons, breast surgeons and surgical oncologists, as well as researchers with an interest in the management of atypical breast lesions. The book will review new data about breast cancer, risk factors for breast cancer, pathological features unique to each entity, the characteristic findings on imaging, risk stratification for genetic testing, as well as the current evidence-based management of each of these breast lesions. Our text will provide assessment tools for risk prediction of breast cancer. We will provide data on the current imaging modalities, as well as advanced screening options available for diagnosis and following these patients. Current management of many of these lesions continues to be controversial in regard to observation with close surveillance versus the need for surgical excision of these lesions based on future risk or whether these lesions are precursor lesion. For ductal carcinoma in-situ, the debate continues in regards to whether this disease entity is a precursor lesion that can be managed with observation or hormonal therapy, or is DCIS cancer and treated with lumpectomy and radiation. Several studies have been published where patients are managed with observation and treatment with hormonal therapy before surgical management. New trials have already begun accruing patients with low to intermediate grade DCIS where patients will be managed with observation versus hormonal therapy only. Management of DCIS continues to evolve and current management will be discussed This text will provide a concise but comprehensive summary of the current management of patients with atypical breast proliferative lesions and some benign breast lesions and will help guided management of these patients. All chapters in this text will be written by experts in the field in each of these disease entities. They will all include the most up to date research and clinical information to enhance our understanding and treatment of patients.