Using a tumour model endogenously expressing high levels of SST2, the present study demonstrated for the first time that the radiolabelled SST antagonist [177Lu]Lu-satoreotide tetraxetan, administered as four fractions of 15 MBq given 1 week apart, suppressed tumour growth and induced tumour regression, prolonged median time taken to reach 850 mm3, and reduced the rate of tumour relapse to a greater degree than [177Lu]Lu-DOTA-TATE administered as four fractions of either 15 or 30 MBq 1 week apart, without inducing a higher toxicity. This evidence concerns the gene SST and neoplasm.