Somatostatin receptor subtype 2 (sst2) is a potential prognostic marker and a therapeutic target in medulloblastoma
Neuroectodermal tumors in general demonstrate high and dense expression of the somatostatin receptor subtype 2 (sst2). It controls proliferation of both normal and neoplastic cells. sst2 has thus been suggested as a therapeutic target and prognostic marker for certain malignancies.
To assess global expression patterns of sst2 mRNA, we evaluated normal (n = 353) and tumor tissues (n = 340) derived from previously published gene expression profiling studies. These analyses demonstrated specific upregulation of sst2 mRNA in medulloblastoma (p < 0.001). sst2 protein was investigated by immunohistochemistry in two independent cohorts.
Correlation of sst2 protein expression with clinicopathological variables revealed significantly higher levels in medulloblastoma (p < 0.05) compared with CNS-PNET, ependymoma, or pilocytic astrocytoma. The non-SHH medulloblastoma subgroup tumors showed particularly high expression of sst2, when compared to other tumors and normal tissues. Furthermore, we detected a significant survival benefit in children with tumors exhibiting high sst2 expression (p = 0.02) in this screening set. A similar trend was observed in a validation cohort including 240 independent medulloblastoma samples.
sst2 is highly expressed in medulloblastoma and deserves further evaluation in the setting of prospective trials, given its potential utility as a prognostic marker and a therapeutic target.