Background: O-LAR 20 to 30 mg IM monthly (qM) is approved for the management of symptomatic NETs. While higher doses are sometimes used for improved symptom control, the benefit of this is not well described. The objectives of the study were to evaluate pre-DI and post-DI symptom, biomarker and tumor size among patients who received O-LAR 40-60 mg qM. Methods: With approval of the BC Cancer Agency research ethics committee the charts of all referred patients with NETs who received O-LAR 40-60 mg qM between 2005 and 2001 were reviewed. Symptom severity was graded on a 4 point scale and any post-increase improvement from grade 2,3 or 4 to 1 or no symptoms was classified an improvement. Pre-DI Chromogranin A (CGA) and 24-hour urine 5-HIAA were compared with the median of 3 post-DI levels and a 10% decrease was classified as a decrease. Results: A total of 37 patients received DI therapy with 40 mg (36), 50 mg (3), and 60 mg (16), for a total of 55 DI events. Median age was 60 and 49, 19, 32% had a tumor of small bowel, pancreas, other, respectively. Post-DI CGA and 5 HIAA levels decreased in 31% (15/49) and 23 % of patients (8/35) respectively. Symptom improvement post DI was observed in 62% (13/21) with diarrhea, 76% (13/17) with flushing, 53% (8/15) with abdominal pain. Post DI, no decreases in tumor size were observed, 29% (14/49) had radiological stable disease and the remainder had progressive tumors. Conclusions: O-LAR 40-60 mg qM was associated with improved symptom control among NET patients with refractory secretory symptoms. CGA and 5-HIAA levels varied in response to DI and were not accurate indicators of symptom control. There was no evidence of tumor regression with O-LAR DI.