Long-term outcomes of 125 patients with stage IV pheochromocytoma or paraganglioma treated with 131I-MIBG

Objectives Available data on treatment of pheochromocytoma or paraganglioma with high dose iodine-131-meta-iodobenzylguanidine (MIBG) is limited by small cohorts and short follow up intervals. We report response and progression-free survival from a cohort of n=125 patients with stage IV pheochromocytoma or paraganglioma treated with palliative 131I-MIBG between 1991 and 2014, with mean follow up of 60 months, total of 593 person-years of follow-up.

Methods Retrospective chart review of a registry of patients receiving median dose 18,833 MBq (509 mCi) 131I-MIBG at an academic tertiary referral center. Imaging response (n=88) was assessed via Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 where imaging was available, or by official imaging report where images were not available for review. Symptom response (n=83) was assessed by chart review of clinical encounters with the oncology service. Lab response (n=50) was defined as 20% change in 2 consecutive values from baseline in catecholamines / VMA, metanephrines or chromogranin A. Following initial MIBG therapy, 32% received additional rounds of MIBG.

Results At first follow up, 75% of patients reported improvement in pre-treatment symptoms, which consisted primarily of pain (60%), fatigue (35%) and hypertension (27%). 39% experienced no symptomatic progression through follow-up; median time to symptomatic progression of was 1.8y ± SE 0.4. Initial follow up imaging demonstrated 1% complete response, 33% partial response, 53% stable disease and 13% progression. 49% of patients showed no post MIBG imaging progression with median time to progression of 2.0y ± 0.6. 59% of patients demonstrated lab response and 24% were stable on initial lab follow up. 50% of patients remained without lab progression after treatment throughout follow-up time, with median time to laboratory progression of 2.8y ± 0.7. Median survival from diagnosis was 11.5y ± 2.4. Median survival following the development of metastatic disease was 6.5y ± 0.8. Survival post treatment was 4.3y ± 0.7. Stable or partial response vs. progression at first imaging follow up predicted improved survival (5.6y ± 0.7 vs. 2.1y ± 1.2, p<0.05).

Conclusions Imaging, symptomatic and laboratory response to high dose 131I-MIBG were achieved on long-term follow up in a large cohort with advanced pheochromocytoma or paraganglioma. Initial response by imaging was associated with prolonged survival. Accordingly, stratification by response at first follow up imaging may be valuable to inform subsequent treatment decisions.