GRP and neuroblastoma: This result was supported by a third study (183) of eight retroperitoneal tumors (including four neuroblastoma/ganglioneuromas, one Wilms tumor, one primitive neuroectodermal tumor, one rhabdoid, and one benign brachial plexus tumor) in which the GRP content in the conditioned media after incubation with each of the tumors was assessed, and it was found the GRP concentration was significantly greater (p=0.003) with all the malignant tumors (including the neuroblastoma) compared to the benign tumors.