Norepinephrine transporter and vesicular monoamine transporter 2 tumor expression as a predictor of response to 131I‐MIBG in patients with relapsed/refractory neuroblastoma

Background Prior studies suggest that norepinephrine transporter (NET) and vesicular monoamine transporter 2 (VMAT2) mediate meta‐iodobenzylguanidine (MIBG) uptake and retention in neuroblastoma tumors. We evaluated the relationship between NET and VMAT2 tumor expression and clinical response to 131I‐MIBG therapy in patients with neuroblastoma. Methods Immunohistochemistry (IHC) was used to evaluate NET and VMAT2 protein expression levels on archival tumor samples (obtained at diagnosis or relapse) from patients with relapsed or refractory neuroblastoma treated with 131I‐MIBG. A composite protein expression H‐score was determined by multiplying a semi‐quantitative intensity value (0–3+) by the percentage of tumor cells expressing the protein. Results Tumor samples and clinical data were available for 106 patients, of whom 28.3% had partial response (PR) or higher. NET H‐score was not significantly associated with response (≥PR), though the percentage of tumor cells expressing NET was lower among responders (median 80% for ≥PR vs. 90% for