Highlights of the San Antonio Breast Cancer Symposium 2019 Part 1: the challenges of tumor heterogeneity

The 42nd annual San Antonio Breast Cancer Symposium (SABCS) was convened in San Antonio Texas on December 10 – 14, 2019. More than 7000 clinicians and scientists from around the world participated in the symposium that featured presentations and keynote talks pertaining to epidemiology and biology, screening/prevention, loco-regional treatment together with systemic therapies for early and late stage disease. This two-part report highlights a selection of important studies presented at this premier breast cancer event with the first part focusing on stromal-epithelial interactions, long term outcomes of hormone replacement therapy, androgen receptor targeting, high risk MRI screening and whether breast surgery can be safely omitted in exceptional responders after neoadjuvant chemotherapy.