Usefulness of (18)F-Fluorodeoxyglucose Positron Emission Tomography for Follow-Up of 13-cis-Retinoic Acid Treatment for Residual Neuroblastoma After Myeloablative Chemotherapy

13-cis-retinoic acid (13-cis-RA) treatment is used as a second-line treatment for residual or recurrent neuroblastoma. However, determining the duration of 13-cis-RA treatment for residual and recurrent neuroblastoma can be a problem because it is difficult to evaluate the effectiveness of the treatment. We performed 13-cis-RA treatment to remove residual active neuroblastoma cells in an 8-year-old boy with stage 4 neuroblastoma that developed from a left sympathetic ganglion and had been treated with chemotherapy, surgery, autologous peripheral blood stem-cell transplantation, and radiotherapy. (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG-PET) and iodine-123 metaiodobenzylguanidine ((123)I-MIBG) scintigraphy obtained immediately before 13-cis-RA treatment both showed positive findings in the area of the primary lesion. At 18 months after 13-cis-RA treatment, there was accumulation on (123)I-MIBG scintigraphy but no uptake on (18)F-FDG-PET, and 13-cis-RA treatment was suspended. The patient has been in complete remission for 3 years. In comparing the effectiveness of the 2 imaging modalities for monitoring the response to 13-cis-RA treatment, we considered that (18)F-FDG-PET was superior to (123)I-MIBG scintigraphy because (18)F-FDG-PET images were not affected by the cell differentiation induced by 13-cis-RA treatment in our case. Thus, (18)F-FDG-PET was useful for determining the treatment response and outcomes. We have reported a case of residual neuroblastoma treated with differentiation-inducing 13-cis-RA therapy. Different results were produced with (18)F-FDG-PET and (123)I-MIBG scintigraphy. The cessation of 13-cis-RA treatment was based on (18)F-FDG-PET findings and there has been no relapse for 3 years.