Objective: To examine treatment trends in invasive lobular carcinoma (ILC) over the last 15 years and, in particular, to compare rates of recurrence and disease-free survival associated with breast conservation therapy compared with mastectomy. Summary Background Data: The biologic characteristics of ILC make it difficult to estimate the extent of the disease by either clinical examination or mammography, and can also make it difficult to detect axillary lymph node metastases. Because of this, there has been a bias toward treating ILC with aggressive therapy. Methods: Patients with ILC were selected from the National Cancer Data Base (1989-2001) using an extensive set of inclusion and exclusion criteria. A total of 21,596 patients were selected, including 8108 who received breast conservation therapy and 13,488 who received mastectomy. Analysis included demographic characteristics, trends in usage of sentinel lymph node biopsy, rates of local and distant recurrence, and 5-year disease-free survival rates. Results: The use of breast conversation therapy increased almost threefold during the study period. From 1998 to 2001, the use of sentinel node biopsy increased more than twofold in the breast conservation group (an average of 23% in 1998 versus 57% in 2001), compared with limited usage in the mastectomy group (an average of 10% in 1998 versus 23% in 2001). Local recurrence rates were very low and disease-free survival rates were correspondingly high in both treatment groups for all diagnosis years and across all pathologic tumor size/lymph node status designations. Conclusions: Less invasive treatment options are becoming widely used for invasive lobular carcinoma, yielding outcomes equivalent to those seen with more aggressive treatment. Copyright © 2005 by Lippincott Williams & Wilkins.