Tandem high-dose 131I-MIBG therapy supported by dosimetry in pediatric patients with relapsed-refractory high-risk neuroblastoma: the Bambino Gesu' Children's Hospital experience

131I-mIBG therapy in relapsed/refractory neuroblastoma: an old bridge to the future

BACKGROUND

The prognosis of relapsed/refractory (R/R) neuroblastoma (NB) is still dismal. The role of iodine-131 meta-iodobenzylguanidine (131I-mIBG) treatment as a tool to reduce tumour burden before novel immunotherapies is not defined.

PATIENTS AND METHODS

Patients with R/R NB were included in a prospective observational study based on two infusions of 131I-mIBG plus melphalan (110 mg/m2), supported by autologous haematopoietic stem cell rescue. The activity of the first administration was 444 MBq (12 mCi/kg), while the second dose was modulated to reach a whole-body absorbed dose of 4 Gy. The International Neuroblastoma Response Criteria (INRC) were used for response.

RESULTS

Twenty-six patients with a median age of 5.9 years (range 2.5-17.2 years) were treated. Twenty-three patients presented a bone/bone marrow involvement, and 21 patients presented an uptake at primary site or at soft-tissue sites. The median International Society of Paediatric Oncology Europe Neuroblastoma Group (SIOPEN) skeletal score was 10 (range 1-70). The main recorded toxicities were haematological, with no toxic deaths and only one grade 4 mucositis. Hypothyroidism was reported in 6 patients of the 14 alive patients. The overall response rate was 48% [95% confidence interval (CI) 28% to 69%] with only one progression; after treatment the median SIOPEN skeletal score was 6 (range 0-70) with a median reduction of 35% (range 4.3%-100%). Overall, 52% (95% CI 32% to 73%) of patients achieved/maintained a SIOPEN skeletal score <7 and a soft-tissue lesion <5 cm was seen in 67% (95% CI 43% to 91%). After this treatment, 65% of patients underwent GD2-targeting chimeric antigen receptor (CAR)-T-cell therapy and 50%, high-dose chemotherapy with busulfan and melphalan. The 3-year overall survival was 55% (95% CI 33% to 73%) and event-free survival was 42% (95% CI 23% to 60%).

CONCLUSION

The 131I-mIBG therapy plus melphalan is confirmed to be effective to reduce/control tumour burden. Further studies are needed to clarify the role and timing of this treatment and to integrate its role in the strategy of CAR-T cells.

Reaching the target dose with one single 131 I-mIBG administration in high-risk neuroblastoma: The determinant impact of the primary tumour

BACKGROUND

131 I-metaiodobenzylguanidine (131 I-mIBG) effectiveness in children with metastasised neuroblastoma (NB) is linked to the effective dose absorbed by the target; a target of 4 Gy whole-body dose threshold has been proposed. Achieving this dose often requires administering 131 I-mIBG twice back-to-back, which may cause haematological toxicity. In this study, we tried identifying the factors predicting the achievement of 4 Gy whole-body dose with a single radiopharmaceutical administration.

MATERIALS AND METHODS

Children affected by metastatic NB and treated with a high 131 I-mIBG activity (>450 MBq (megabecquerel)/kg) were evaluated retrospectively. Kinetics measurements were carried out at multiple time points to estimate the whole-body dose, which was compared with clinical and activity-related parameters.

RESULTS

Seventeen children (12 females, median age 3 years, age range: 1.5-6.9 years) were included. Eleven of them still bore the primary tumour. The median whole-body dose was 2.88 Gy (range: 1.63-4.22 Gy). Children with a 'bulky' primary (>30 mL) received a higher whole-body dose than those with smaller or surgically removed primaries (3.42 ± 0.74 vs. 2.48 ± 0.65 Gy, respectively, p = .016). Conversely, the correlation between activity/kg and the whole-body dose was moderate (R: 0.42, p = .093). In the multivariate analysis, the volume of the primary tumour was the most relevant predictor of the whole-body dose (p = .002).

CONCLUSIONS

These data suggest that the presence of a bulky primary tumour can significantly prolong the 131 I-mIBG biological half-life, effectively increasing the absorbed whole-body dose. This information could be used to model the administered activity, allowing to attain the target dose without needing a two-step radiopharmaceutical administration.

Timing and chemotherapy association for 131-I-MIBG treatment in high-risk neuroblastoma

Prognosis of high-risk neuroblastoma is dismal, despite intensive induction chemotherapy, surgery, high-dose chemotherapy, radiotherapy, and maintenance. Patients who do not achieve a complete metastatic response, with clearance of bone marrow and skeletal NB infiltration, after induction have a significantly lowersurvival rate. Thus, it's necessary to further intensifytreatment during this phase. 131-I-metaiodobenzylguanidine (131-I-MIBG) is a radioactive compound highly effective against neuroblastoma, with32% response rate in relapsed/resistant cases, and only hematological toxicity. 131-I-MIBG wasutilized at different doses in single or multiple administrations, before autologous transplant or combinedwith high-dose chemotherapy. Subsequently, it was added to consolidationin patients with advanced NB after induction, but an independent contribution against neuroblastoma and for myelotoxicity is difficult to determine. Despiteresults of a 2008 paper demonstratedefficacy and mild hematological toxicity of 131-I-MIBG at diagnosis, no center had included it with intensive chemotherapy in first-line treatment protocols. In our institution, at diagnosis, 131-I-MIBG was included in a 5-chemotherapy drug combination and administered on day-10, at doses up to 18.3 mCi/kg. Almost 87% of objective responses were observed 50 days from start with acceptable hematological toxicity. In this paper, we review the literature data regarding 131-I-MIBG treatment for neuroblastoma, and report on doses and combinations used, tumor responses and toxicity. 131-I-MIBG is very effective against neuroblastoma, in particular if given to patients at diagnosis and in combination with chemotherapy, and it should be included in all induction regimens to improve early responses rates and consequently long-term survival.