PGR and breast carcinoma: PR imaging has been evaluated using the steroidal PR ligand, 21-[18F]fluorofuranyl-norprogesterone ([18F]FFNP) in primary breast carcinoma as well as reporting on treatment response in subsequent in vivo animal studies (Chan et al., 2015, Dehdashti et al., 2012, Fowler et al., 2012).