Addressing overtreatment of screen detected DCIS; the LORIS trial

Abstract Overdiagnosis, and thus overtreatment, are inevitable consequences of most screening programmes; identification of ways of minimising the impact of overdiagnosis demands new prospective research, in particular the need to separate clinically relevant lesions that require active treatment from those that can be safely left alone or monitored and only need treated if they change characteristics. Breast cancer screening has led to a large increase in ductal carcinoma in situ (DCIS) diagnoses. This is a widely heterogeneous disease and most DCIS detected through screening is of high cytonuclear grade and therefore likely to be important clinically. However, the historic practice of surgical treatment for all DCIS is unlikely to be optimal for lower risk patients. A clearer understanding of how to manage DCIS is required. This article describes the background and development of ‘The low risk’ DCIS trial (LORIS), a phase III trial of surgery versus active monitoring. LORIS will determine if it is appropriate to manage women with screen detected or asymptomatic, low grade and intermediate grade DCIS with low grade features, by active monitoring rather than by surgical treatment.