Neuroendocrine tumors in the brain

Somatostatin and other neuropeptides are expressed in tumors originating fr om neuronal precursors and paraganglia, namely medulloblastoma, central Pri mitive Neuro-Ectodermal Tumors (cPNETs), neurocytoma, gangliocytoma, olfact ory neuroblastoma, paraganglioma. In medulloblastoma, the most common malig nant tumor in childhood, there is an extensive expression of somatostatin i n addition to somatostatin receptors (SSTR) type 2. Although density of SST R-2 and intensity of expression of somatostatin genes have no prognostic si gnificance in medulloblastoma, their presence may bring along important inf ormation on oncogenesis and relate medulloblastoma to cPNETs. Radio-labeled octreotide scintigraphy may be useful in the follow-up of these patients, allowing differentiation between scar and tumoral tissue. Moreover, on the basis of octreotide-induced inhibition of cell proliferation in medulloblas toma, a trial with octreotide in patients with recurrent or high-risk tumor is warranted. Meningiomas and low-grade astrocytic gliomas, even if not di splaying a clear neuroendocrine phenotype, have high levels of SSTR-2. In m eningiomas, SSTRs-scintigraphy is not part of the routine pre-operative ass essment; moreover, a therapeutic trial with somatostatin-analogues in patie nts with recurrent or inoperable meningiomas should be carried-out with gre at caution, because somatostatin and octreotide slightly increase cell prol iferation in cultured meningiomatous cells. Low-grade gliomas (WHO grade 2) , and a smaller fraction of anaplastic astrocytomas, express SSTR-2, while glioblastomas usually do not. Unfortunately, radiolabeled-octreotide scinti graphy is not useful in the differential diagnosis of gliomas, because the results are altered by the disruption of the blood brain barrier (BBB); in addition, radionuclide-labeled somatostatin analogues are not useful in the therapy of low-grade gliomas, because the intact BBB prevents them from re aching the target SSTR-2. Recently, a pilot study in gliomas, has proposed the use of a radio-labeled somatostostatin analogue with a loco-regional ap proach in order to overcome the intact BBB.