In situ carcinomas of the breast: Ductal carcinoma in situ and lobular carcinoma in situ

Over the past several decades, the widespread adoption of mammographic screening has had a significant impact on the incidence, diagnosis, classification, and treatment of all breast diseases. These changes have been particularly profound for in situ carcinoma of the breast. As a result, there has been a vast increase in the number of publications in the literature with regard to the definition, diagnostic criteria, and both short-term and long-term risks associated with specific histologic variants or types of in situ carcinoma of the breast. It is estimated that by 2020, approximately 1 million women will be living with DCIS-more than double the number in 2005. In situ carcinomas of the breast were first recognized in the early 20th century and were identified morphologically as cells cytologically similar to those of invasive carcinomas but confined to ductal structures within the breast parenchyma. Such lesions were generally found to be located adjacent to areas of invasive carcinoma. The original definitions given to in situ carcinomas of the breast were arbitrary. Opportunities to study the natural history and behavior of such in situ lesions independent of an invasive component of disease or after a surgical procedure less than that of mastectomy were previously rarely encountered. Since that time, several studies relying on the review of archival slide material have demonstrated basic differences between distinct histologic patterns of in situ carcinomas. This subsequently resulted in the distinction between those lesions representing purely markers of increased risk (e.g., lobular carcinoma in situ [LCIS] and atypical hyperplasia, with increased breast cancer risk that was essentially equally distributed to either breast) and committed premalignant lesions (e.g., ductal carcinoma in situ [DCIS], with increased breast cancer risk that was more often reported to be confined to the ipsilateral breast).