Ductal carcinoma in situ (DCIS) accounts for approximately 20% of mammographically detected breast cancers. DCIS can recur or progress to invasive breast cancer, but the ability to predict the outcome of patients with DCIS remains limited, leading to inappropriate treatment choices. To the authors' knowledge to date, the hunt for molecular prognostic markers for DCIS has been unsuccessful. Emerging technologies, however, are shedding new light on the biologic course of DCIS. In the current study, the authors review recent findings elucidating the molecular journey from DCIS to invasive cancer and discuss how these findings will lead to more effective treatment with minimization of morbidity. (c) 2008 American Cancer Society.