Highlights of the San Antonio Breast Cancer Symposium 2015: part 1.

38th San Antonio Breast Cancer Symposium, San Antonio, TX, USA, 8-12 December 2015 The 38th annual San Antonio Breast Cancer Symposium (SABCS) was convened in San Antonio (TX, USA) on 8-12 December 2015. More than 7000 clinicians and scientists from around the world participated in the symposium, which featured a range of presentations and keynote talks pertaining to breast cancer screening, prevention, loco-regional and systemic therapies. This two-part report highlights a selection of important studies presented at this premier breast cancer event with part 1 focusing on radiotherapy treatment, translational approaches to immunotherapy and longer term cardiotoxicity from anti-HER2 therapies. The second part of this report will discuss a range of topics including de-escalation of chemotherapy regimens in luminal A tumors, the prognostic relevance of circulating tumor cells, the optimum treatment of triple-negative breast cancer and shifting attitudes to primary surgical treatment.