Differential expression of sst1, sst2A, and sst3 somatostatin receptor proteins in low-grade and high-grade astrocytomas.

We have previously reported that sst2A somatostatin receptors are frequently overexpressed in human meningiomas. Initial clinical observations suggest that somatostatin analogues may also be of value for imaging and treatment of other human intracranial tumors, including astrocytomas. However, contradictory results have been reported regarding the expression of somatostatin receptors in low-grade and high-grade astrocytomas. Therefore, we determined the precise pattern of somatostatin receptor protein expression in 8 diffuse astrocytoma (DA), 10 anaplastic astrocytomas (AA), and 32 glioblastoma multiforme (GBM) using immunohistochemistry and Western blot analysis. sst1 and sst2A somatostatin receptors were not present in DA and only occasionally detected in AA. In GBM, sst1 was present in 66%, and sst2A was found in 44% of the tumors. sst3 receptors were present in 38% of DA, 40% of AA, and 84% of GBM. Thus, loss of differentiation was significantly associated with increased expression of sst1, sst2A, and sst3 somatostatin receptors. In contrast, sst4 and sst5 receptors were found in 80% and 25% of all cases, respectively, in a manner independent of histological grade. No significant correlation was found between somatostatin receptor expression and the proliferation rate of the tumors as determined by MIB-I immunostaining. Furthermore, the presence or absence of the 5 somatostatin receptor subtypes did not significantly influence survival time in 14 GBM patients.