Although
somatostatin receptors have been detected in many normal and neoplastic tissues, little is known of their expression and function in
peripheral nerve tumors. In the present study, we examined the expression of all 5
somatostatin receptor subtypes (sst1-5) in 3 normal peripheral nerves, 3 traumatic
neuromas, 27
schwannomas, 18
neurofibromas, and 177
malignant peripheral nerve sheath tumors (MPNSTs) by immunohistochemistry as well as by Western blot and
reverse transcriptase-polymerase chain reaction investigations in 2 normal peripheral nerves, one
neurofibroma, 5
schwannomas, and 5 MPNSTs. Immunoreactive
somatostatin receptors were not detectable in normal peripheral nerve and in nonneoplastic Schwann cell proliferations. In contrast, sst2A
mRNA and
protein was present in 89% of
schwannomas. This receptor subtype was less frequently detected in
neurofibromas (22%) and MPNSTs (15%). Interestingly, sst4 was seen in 32% of MPNSTs and was almost exclusively expressed in this malignant
tumor type. In support of a role in Schwann cell
tumor growth control by
somatostatin was the observation of induced internalization of sst2A and inhibition of cell proliferation in an NF1-associated
MPNST cell line. Moreover, administration of an sst2A-selective agonist resulted in induction of
MPNST cell apoptosis. We conclude that
peripheral nerve sheath tumors often express at least one functional
somatostatin receptor. Furthermore, our findings suggest a potential clinical role for
somatostatin receptor agonists in
tumor imaging and/or treatment of
schwannomas and MPNSTs.