Predictors of survival in 211 patients with stage IV pulmonary and gastroenteropancreatic mIBG positive neuroendocrine tumors treated with I-131 mIBG.

Abstract

Purpose: This retrospective analysis identifies predictors of survival in a cohort of patients with mIBG positive stage IV pulmonary and gastroenteropancreatic neuroendocrine tumor (P/GEP-NET) treated with I-131 mIBG therapy, in order to inform treatment selection and post-treatment monitoring. Methods: Survival, symptoms, imaging, and biochemical response were extracted via chart review from n = 211 P/GEP-NET patients treated with mIBG between 1991-2014. For patients with computed tomography (CT) follow up (n = 125), imaging response was assessed by Response Evaluation Criteria on Solid Tumors (RECIST) 1.1 where images were available (n = 76) or by chart review of the radiology report where images could not be reviewed (n = 49). Kaplan Meier analysis and Cox multivariate regression estimated survival and progression free survival benefits predicted by initial imaging, biochemical and symptomatic response. Results: All patients had stage IV disease at time of treatment. Median survival was 29 months from time of treatment. 71% of patients demonstrated symptomatic response with median duration of symptomatic relief of 12 months. Symptomatic response at first follow-up predicted a survival benefit of 30 months (p<0.001). Biochemical response at first clinical follow up was seen in 34% of patients with stability of labs in 48%; response/stability vs. progression extended survival 40 months (p<0.03). Imaging response (20% of patients) or stability (60%) at initial 3 month follow up imaging extended survival 32 months (p<0.001). Additionally, multiple mIBG treatments was associated with 24 months additional survival (p<0.05). Conclusion: Therapeutic I-131-mIBG for metastatic pulmonary or gastroenteropancreatic neuroendocrine tumors appears to be an effective means of symptom palliation. Imaging, biochemical, and symptomatic follow-up each help prognosticate expected survival following mIBG therapy. Multiple rounds of mIBG are associated with prolonged survival; it is unclear whether this represents cause or effect.