The causes of exclusion were as follows: PET-CT not performed prior to surgery (n = 8), metastatic tumors on initial staging (n = 4), missing data (n = 1), breast lesions not 18F-FDG avid (n = 3), hormonal receptors (ER and PR) negative tumors (n = 7), IHC slide unusable (n = 1), and volume of interest too small to be analyzed with LifeX software (n = 1). The gene discussed is ESR1; the disease is metastatic neoplasm.