Background: To evaluate the radiological and clinical therapeutic effectiveness of ^{90}Y-octreotate [DOTATATE] inpatients with progressive somatostatin receptor-positive midgut neuroendocrine carcinomas (GEPNETs). Material/Methods: The study group: 34 patients, with histological proven extensive non-resectable and progressive midgut GEP-NETs. Radionuclide therapy (^{90}Y-DOTATATE) was given i.v. with a mean activity per administration 3,82 GBq. Initial clinical tumor responses were assessed 6-7 weeks after therapy completion and then once 3-monthly. The objective tumor response was classified according to the RECIST, initially between 4-6 months and then after each of the 6 months interval. Results: At 6 months after treatment completion, radiological tumor response was observed in 6 subjects with PR (19%), 25 presented SD (78%) and single had PD (3%). Overall clinical response to therapy at 6 months follow-up was observed in 23 patients (68%), SD in 5 patients (15%) and PD in 6 (18%). A year after therapy radiological tumour response was seen in 11 patients (44%), SD had 12 subjects (44%) and DP was noted in 2 patients. Two years after completed therapy PR was seen in 6 patients (33%), SD in additional 11 subjects (61%), single patient had PD. Clinical response to treatment in terms of PR and SD were noted in 22 patients (88%) after 1 year and in 14 patients (87%) after 2 years. Median PFS was 20 months, while the median OS was 23 months. In the 6 patients with clinical PD within initial 6 months the median PFS was 6 months and OS 11 months, while in those with SD or PR PFS was 22 months and OS 26 months (P<0.05). Conclusions: Therapy with ^{90}Y-DOTATATE} is effective in terms of clinical response, however the radiological response measured by the RECIST criteria underestimates benefits of this type of therapy in patients with progressive somatostatin receptor-positive midgut neuroendocrine carcinomas
