Abstract BACKGROUND: Neuroendocrine neoplasms (NENs) are a heterogenous group of tumors originating from neuroendocrine cells. These can occur anywhere in the body where neuroendocrine cells exist, but the most common sites are the gastrointestinal tract, the broncopulmonal system and the pancreas (P-NEN). By using Ki-67% as a proliferation index it is possible to categorize all the neoplasms into WHO-grades. Surgery is the only curative therapy, but at the time of diagnosis about 50% of all patients are inoperable as they have disseminated disease. The chemotherapy combination streptozocin and 5-fluorouracil (STZ/5-FU) is one of the palliative treatment modalities for this patient group. The evidence of the effect of this treatment is based on small retrospective studies. AIMS: To evaluate the effect of STZ/5-FU on patients with neuroendocrine neoplasms in an everyday practice at Oslo University Hospital and in published studies. METHOD: We retrospectively evaluated medical records and radiological and biochemical reports of 81 patients that initiated STZ/5-FU as treatment for NENs at Center for neuroendocrine tumors, Section for Gastroenterology, Department of Transplantation Medicine, Oslo University Hospital during April 2007 and May 2017. We compared our results with two other retrospective studies of patients with pancreatic-NEN that received the same chemotherapy combination. RESULTS: Seventy-two patients where evaluable and 9 patients were excluded from the analysis. The median progression free survival from the last CT (computed tomography) image before treatment initiation was 11 months and median overall survival was 99 months. Disease control rate (objective response + stable disease) was 59.7%. Regression as the best radiological response was achieved in 27 (37.5%) patients and stabile disease was seen in 16 (22.2%). Altogether 29 (40.3%) patients had no effect of the treatment as they had progressive diseases at first follow-up examination after initiation of the therapy. The treatment was well tolerated, but 72.2% of the patients experienced side effects and 16.6% had to discontinue the therapy because of these side effects. Five (6.9%) patients died during treatment, but no treatment associated death was observed. CONCLUSION: In our population, we found a disease control rate of 60%, which means that the majority of the patients that were given this treatment, halted the advancement of the disease for a period of time. The treatment was well-tolerated and only a few patients had to stop because of side effects. The studies reported in literature differed in patient populations as well as methods of radiolaWe found no directly comparable studies (differing in patient populations and methods of radiological assessments). However, randomized and controlled prospective studies are needed to directly compare the efficacy and toxicity of STZ/5-FU in treatment of NENs.