Iodine-131--metaiodobenzylguanidine double infusion with autologous stem-cell rescue for neuroblastoma: a new approaches to neuroblastoma therapy phase I study

Abstract

Purpose: Iodine-131-metaiodobenzylguanidine ((131)I-MIBG) provides targeted radiotherapy with more than 30% response rate in refractory neuroblastoma, but activity infused is limited by radiation safety and hematologic toxicity. The goal was to determine the maximum-tolerated dose of (131)I-MIBG in two consecutive infusions at a 2-week interval, supported by autologous stem-cell rescue (ASCR) 2 weeks after the second dose.

Patients and methods: The (131)I-MIBG dose was escalated using a 3 + 3 phase I trial design, with levels calculated by cumulative red marrow radiation index (RMI) from both infusions. Using dosimetry, the second infusion was adjusted to achieve the target RMI, except at level 4, where the second infusion was capped at 21 mCi/kg.

Results: Twenty-one patients were enrolled onto the study at levels 1 to 4, with 18 patients assessable for toxicity and 20 patients assessable for response. Cumulative (131)I-MIBG given to achieve the target RMI ranged from 22 to 50 mCi/kg, with cumulative RMI of 3.2 to 8.92 Gy. No patient had a dose-limiting toxicity. Reversible grade 3 nonhematologic toxicity occurred in six patients at level 4, establishing the recommended cumulative dose as 36 mCi/kg. The median time to absolute neutrophil count more than 500/microL after ASCR was 13 days (4 to 27 days) and to platelet independence was 17 days (6 to 47 days). Responses included two partial responses, eight mixed responses, three stable disease, and seven progressive disease. Responses by semiquantitative MIBG score occurred in eight patients, soft tissue responses occurred in five of 11 patients, but bone marrow responses occurred in only two of 13 patients.

Conclusion: The lack of toxicity with this approach allowed dramatic dose intensification of (131)I-MIBG, with minimal toxicity and promising activity.

Conflict of interest statement

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

Figures

Fig 1.

Patient N066 with refractory neuroblastoma treated at dose level 4 on day 0 (709 mCi; cumulative red marrow radiation index [RMI], 4.74 Gy) and day +14 (497 mCi; RMI, 4.18 Gy). (A) Iodine-123—metaiodobenzylguanidine (MIBG) scan pretherapy and on day +56 post therapy. Pretherapy scan showed multiple sites of skeletal uptake throughout the spine, pelvis, femurs, and humeri, with physiologic uptake in salivary glands, nasopharynx, liver, and bladder. The post- therapy day +56 scan showed only very faint uptake in the left proximal humerus and left pelvis and the usual physiologic uptake. (B) Iodine-131—MIBG uptake immediately after therapy 1 (day +3) and 2 (day +17).

Fig 2.

Overall survival and progression-free survival (PFS) of all 21 patients with median follow-up for all patients at 16 months, and surviving patients at 28 months. PFS was calculated regardless of subsequent therapy.