Breast cancer screening aims to detect breast cancer at an earlier stage than they would otherwise be detected to improve survival. In the UK this is based on regular mammographic examinations, and has been in existence for over 30 years with a number of changes over that time. Currently the UK National Health Service Breast Screening Programme consists of 3 yearly, 2-view mammography for all women between the ages of 50 and 70. Screen-detected cancers are commonly small tumours with no axillary nodal involvement, and around a quarter are non-invasive Ductal carcinoma in situ (DCIS). The treatment of cancers detected through screening is the same as for symptomatically detected breast cancers. The profile of screen-detected breast cancers means that primary surgery, with either Breast-conserving surgery or mastectomy, is the mainstay of treatment. Breast-conserving surgery (BCS) is prevalent, and often requires the use of localisation—of which there are an increasing number—to help guide precise surgery. As imaging modalities have improved, the size of breast cancers diagnosed through screening has reduced. There is much interest in the de-escalation of treatment, and particularly surgery, in these low-risk cancers. Recently reported, or ongoing trials, are investigating percutaneous procedural–based interventions for the treatment of breast lesions and the omission of axillary staging surgery. A number of studies are investigating active surveillance rather than excisional treatment of low-risk DCIS. This chapter gives an outline and an update on treatment of screen-detected cancers.