LAUSR

OBJECTIVES Fluorescence-guided surgery (FGS) may improve completeness of resection in transsphenoidal surgery for Cushing's Disease (CD) by enabling visualization of residual tumor tissue at the margins. In this review we discuss somatostatin receptors (SSTRs) as targets for FGS and overview existing SSTR-specific imaging agents. We also compare SSTR expression in normal pituitary and corticotrophinoma tissues from human and canine CD patients to assess canines as a translational model for CD. METHODS A PubMed literature search was conducted for publications containing the terms canine, somatostatin receptor, Cushing's Disease, and corticotroph adenoma. SSTR expression data from each study was documented as the presence or absence of expression, or when possible, the number of tumors expressing a given SSTR subtype within a group of tumors being studied. Studies that used RT-PCR to quantify SSTR expression were selected for additional comparative analysis. RESULTS SSTR5 is strongly expressed in human corticotroph adenomas and weakly expressed in surrounding pituitary parenchyma, a pattern not conclusively observed in canine patients. SSTR2 mRNA expression is similar in human normal pituitary and corticotrophinoma cells, but may be significantly higher in canine normal pituitary tissue than in corticotroph tumoral tissue. Limited data was available on SSTR subtypes 1, 3, and 4. CONCLUSIONS Further studies must fill the knowledge gaps related to species-specific SSTR expression, thus using canine CD as a translational model may be premature. We do conclude that the expression profile of SSTR5 (i.e. high local expression in pituitary adenomas relative to normal surrounding tissues) makes SSTR5 a promising molecular target for FGS.