Similar to prostate cancer, the FDG avidity of breast cancer is variable and depends on its histologic and biologic characteristics, where invasive ductal carcinomas, higher grade, and triple-negative tumors (i.e. tumors which lack estrogen receptors (ER), progesterone receptors (PR), and human epidermal growth factor receptors 2 (HER2) typically show more intense tracer uptake (Yoon et al., 2014). Here, PGR is linked to breast cancer.