Immunohistochemical Detection of Somatostatin Receptors in Human Ovarian Tumors

Abstract

Objective. It is well established that many human tumors can express somatostatin receptors. This is the molecular basis for the application of long-acting somatostatin analogues for therapeutic and diagnostic purposes. However, there are discrepancies in earlier studies regarding the prevalence of somatostatin receptor expression in human ovarian tumors detected using autoradiographic binding studies or reverse transcription-polymerase chain reaction.Methods. We have previously developed a panel of somatostatin receptor subtype-specific antibodies that effectively stain formalin-fixed, paraffin-embedded human tumor tissue. In the present study, we have used these antibodies to determine the somatostatin receptor status of 47 randomly selected human ovarian tumors.Results. Somatostatin receptor-like immunoreactivity was in most cases located at the plasma membrane as well as in the cytoplasm of the tumor cells and was completely blocked with antigenic peptide. The pattern of expression of somatostatin receptor subtypes varied greatly between individual tumors. Of the 47 ovarian tumor specimens analyzed, 9 tumors (∼19%) were positive for sst1, 13 (∼28%) revealed immunoreactive sst2A receptors, 20 (∼42%) showed sst3-like immunoreactivity, 8 (∼17%) revealed immunoreactive sst4 receptors, and 10 (∼21%) were positive for sst5. Whereas 18 tumors (∼38%) revealed no somatostatin receptor immunoreactive staining, 14 (∼30%) expressed more than one somatostatin receptor subtype. The expression of somatostatin receptor subtypes was independent of patient age, diagnosis, and histological grade.Conclusion. We provide direct evidence of somatostatin receptor protein expression in human ovarian tumors. Our findings suggest that a subgroup of receptor-positive ovarian tumors may be a potential target for treatment with somatostatin receptor subtype-selective analogs. However, due to the wide variations in the somatostatin receptor status of similar cases, each tumor specimen must be tested individually for the presence of particular somatostatin receptor subtypes.