Somatostatin-based radiotherapy with [(90)Y-DOTA]-TOC in neuroendocrine tumors: long-term outcome of a phase I dose escalation study

BACKGROUND: We describe the long-term outcome after clinical introduction and dose escalation of somatostatin receptor targeted therapy with [(90)Y-DOTA]-TOC in patients with metastasized neuroendocrine tumors. METHODS: In a clinical phase I dose escalation study we treated patients with increasing [(90)Y-DOTA]-TOC activities. Multivariable Cox regression and competing risk regression were used to compare efficacy and toxicities of the different dosage protocols. RESULTS: Overall, 359 patients were recruited; 60 patients were enrolled for low dose (median: 2.4 GBq/cycle, range 0.9-7.8 GBq/cycle), 77 patients were enrolled for intermediate dose (median: 3.3 GBq/cycle, range: 2.0-7.4 GBq/cycle) and 222 patients were enrolled for high dose (median: 6.7 GBq/cycle, range: 3.7-8.1 GBq/cycle) [(90)Y-DOTA]-TOC treatment. The incidences of hematotoxicities grade 1–4 were 65.0%, 64.9% and 74.8%; the incidences of grade 4/5 kidney toxicities were 8.4%, 6.5% and 14.0%, and the median survival was 39 (range: 1–158) months, 34 (range: 1–118) months and 29 (range: 1–113) months. The high dose protocol was associated with an increased risk of kidney toxicity (Hazard Ratio: 3.12 (1.13-8.59) vs. intermediate dose, p = 0.03) and a shorter overall survival (Hazard Ratio: 2.50 (1.08-5.79) vs. low dose, p = 0.03). CONCLUSIONS: Increasing [(90)Y-DOTA]-TOC activities may be associated with increasing hematological toxicities. The dose related hematotoxicity profile of [(90)Y-DOTA]-TOC could facilitate tailoring [(90)Y-DOTA]-TOC in patients with preexisting hematotoxicities. The results of the long-term outcome suggest that fractionated [(90)Y-DOTA]-TOC treatment might allow to reduce renal toxicity and to improve overall survival. TRIAL REGISTRATION: ClinicalTrials.gov number:NCT00978211