In this study, using the AR42J tumour model, we have evaluated the in vivo efficacy and safety of the SST2 antagonist [177Lu]Lu-satoreotide tetraxetan, administered for four cycles at a radioactivity of 15 MBq per cycle, compared with the agonist [177Lu]Lu-DOTA-TATE given for four cycles at either 15 or 30 MBq per cycle, i.e., a human equivalent dose of 3.7 or 7.4 GBq per cycle. The gene discussed is SSTR2; the disease is neoplasm.