In a study of patients with localized luminal/HER2-negative breast cancer for whom breast-conserving surgery was initially not feasible and NAC was prescribed to reduce tumor, Grapin et al. found that breast size (women with a total breast volume higher than 496 mL, quantified precisely on the coregistration CT of the PET system) and tumor chemosensitivity (positive metabolic response after the first cycle of treatment, defined by ΔMTV-17%) were the two main predictive imaging parameters of breast-conserving surgery. The gene discussed is ERBB2; the disease is breast cancer.