The advantage of this technique is that it is relatively rapid, it leads to efficient engraftment of neuroblastoma cell lines and there is no morbidity associated with the technique. Five human NB cell lines were chosen to demonstrate the feasibility and utility of this approach – NB5, NB7, NB1691, SKNAS and SKNSH. These cell lines were selected because they differ in Nmyc amplification, caspase-8 expression, p53 Torin 1 mutation status and 1p36 LOH. The cells were labeled with luciferase by stable transfection with a retrovirus expressing the luciferase gene. Luciferase expression was tested and quantified in the Xenogen Imager before injecting the cells into the mice. Single suspension cells were mixed with matrigel in a total volume of 10 ml and implanted into the para-adrenal area, between the adrenal and the kidney or into the adrenal medulla itself. Injections were done with the aid of an BMS-354825 ultrasound-guided catheter and needle. Tumor formation and growth was monitored for up to 24 weeks. Orthotopic ultrasound guided xenografts faithfully recapitulated many of the histological hallmarks of neuroblastoma. Xenografts showed some heterogeneity in terms of cell size and immunohistochemical staining patterns, and the presence of cells with a more differentiated somewhat ganglionlike appearance in tumors from some but not all cell lines. Similar to the mouse tumors, all tumors of the xenografts tumors stained positive for the neuroendocrine marker PGP 9.5. Mitotic figures were consistently seen and proliferation, indicated by Ki67, was notably greater in areas around blood vessels and at the peripheral margins of the tumor. Regions of xenografts were also immunoreactive for synaptophysin, neuron specific enolase and tyrosine hydroxylase, however; these markers were not as ubiquitously expressed as PGP 9.5. Electron microscopy also demonstrated that the xenograft tumors resembled the human N-MYC amplified tumors as well as the murine TH-MYCN tumors. The human xenograft tumors contained areas enriched in dense core synaptic vesicles and synapses and junction typical of neuronal cells. There were also areas of lipids dispersed throughout the tumors. Tumor growth was monitored by sequential Xenogen imaging. Growth curves generated from this data are shown in Figure 3. Paradrenal xenografts established from cell line NB1691 showed the most aggressive growth rates reaching a tumor volume. NB5 paradrenal xenografts grew slightly slower, reaching a volume of when transplanted into the retroperitoneal space near the adrenal or 36+/23.5 days when injected directly into the adrenal gland. The remainder of SKNSH xenografts either failed to engraft or regressed. Similarly, NB7 xenografts demonstrated inconsistent engraftment and growth with only mouse tumors reaching a volume of 600 mm3, one after 43 days and the other after 142 days.