- Persistence of disease after at least a partial response to frontline therapy (i.e. patient has had at least a partial response to frontline therapy but still has residual disease by MIBG scan, CT/MRI, or bone marrow aspirate/biopsies). Patients in this category are REQUIRED to have histologic confirmation of viable NB from at least one residual site. Tumor seen on routine bone marrow morphology is sufficient.