MKI67 and breast cancer: The results of a phase 1 clinical trial (NCT00968656) published in 2013 demonstrated a high correlation between S2R ligand [18F]ISO-1 and Ki-67 (i.e., a common measure of the proliferative activity of breast cancer cells) in patients with breast cancer, head and neck cancer, and lymphoma, thereby indicating that [18F]ISO-1 shows promise for the evaluation of the proliferative status of solid tumors [20].