PGR and breast cancer: Consistently, in the pilot C-BOBCAT trial, which examined [64Cu]Cu-SAR-bombesin (a comparable GRPR antagonist peptide), PET imaging in female patients with recurrent metastatic estrogen receptor–positive/progesterone receptor–positive/human epidermal growth factor receptor 2–negative breast cancer revealed initial uptake of the peptide by the pancreas with a rapid washout between 4 and 24 h, whereas high and strong retention in tumor lesions was visualized up to at least 24 h (30).