<b>Conclusions</b>: The preclinical and clinical results confirm the feasibility of [<sup>177</sup>Lu]Lu-DOTA-MGS5 PRRT in patients with SCLC and support further clinical studies investigating the therapeutic value and clinical applicability of this new CCK2R-targeted theranostic approach in larger patient cohorts. This evidence concerns the gene CCKBR and small cell lung carcinoma.