The programme will continue the long-running Early Breast Cancer Triallists’ Collaborative Group (EBCTCG) and the ATLAS trial follow-up to obtain large-scale randomised evidence about the long-term main effects and side-effects of local and systemic adjuvant breast cancer treatments, and influence the interpretation of past trials and the design of future trials of treatment and screening. About every 5 years, EBCTCG seeks data on each individual patients in all adjuvant breast trials, for checking and meta-analyses and has previously demonstrated effects on mortality not reliably demonstrable in separate trials. EBCTGCG reports (>14,000 citations) influence practice guidelines and change worldwide treatment patterns. The long-term survival gains identified are each only moderate, but, from the combination of several moderate gains, UK breast cancer mortality at age 35-69 has been halved. The collaboration has also shown that 5-year tamoxifen reduces 10-year and 15-year breast cancer mortality rates by 1/3. It was feared that continuing tamoxifen for more than 5 years might increase rather than decrease recurrence, but CTSU’s ATLAS trial (n=13,000) randomised 10-year vs 5-year tamoxifen and showed 10-year continuation moderately lowers 15-year mortality. Follow-up of ATLAS is continuing, as ER+ disease can recur throughout years 10-20.