Immunohistochemical determination of five somatostatin receptors in meningioma reveals frequent overexpression of somatostatin receptor subtype sst(2A)

Meningioma is one of a variety of human tumors that exhibit a very high den sity of somatostatin receptors and in many cases show a true positive somat ostatin receptor scintigraphy, However, the level of expression of individu al somatostatin receptor proteins in meningioma has not been investigated. We have recently developed a panel of somatostatin receptor subtype-specifi c antibodies that effectively stain formalin-fixed, paraffin-embedded tumor tissue (S, Schulz et at, Clin, Cancer Res., 4: 2047-2052, 1998), In the pr esent study, me have used these antibodies to determine the somatostatin re ceptor status of 30 randomly selected meningiomas, Immunoreactive staining for all somatostatin receptors was clearly located at the plasma membrane o f the tumor cells and completely blocked with antigenic peptide. The vast m ajority of tumors (29 cases; 70%) mere positive for sst(2A), immunoreactivi ty; among these, 20 (69%) tumors showed high levels of sst,, immunoreactivi ty. In contrast, all other somatostatin receptors were only detected sporad ically, and none of these cases revealed a particularly strong staining, Ho wever, it is uncertain to what extent somatostatin receptor-immunoreactive staining intensity may translate into somatostatin receptor protein express ion on the tumor cells. Therefore, in a prospective study, 16 surgically re moved meningiomas were collected, and the level of sst(2A), expression was determined using Western blot analysis, Whereas sst(2A) was readily detecta ble as a broad band migrating at M-r, 70,000 in 12 (75%) of these tumors, 8 tumors (50%) showed particularly high levels of immunoreactive sst,, recep tors, There was an excellent correlation (P < 0.001) between the level of s st(2A) protein expression detected in Western blots and the sst(2A)- immuno reactive staining seen in tissue sections, Thus, the frequent overexpressio n of the sst(2A) receptor may explain the high tracer uptake often observed in meningioma patients during somatostatin receptor scintigraphy, Moreover , this simple immunohistochemical method could prove useful in identifying those cases of recurrent disease that may possibly respond to therapy with sst(2)-selective agonists.