ESR1 and breast cancer: During the workshop, a preclinical study in estrogen receptor positive (ER +) patient-derived breast cancer xenografts treated with a phosphoinositide 3-kinase (PI3K) inhibitor was presented which demonstrated that hyperpolarized [1-13C]pyruvate detected response where none could be detected using fluorodeoxyglucose-18 positron emission tomography (18F-FDG-PET).