In Vivo Versus In Vitro Somatostatin Receptor Expression in Neuroendocrine Neoplasms: A Systematic Review and Meta-Analysis of Correlation Studies

Well-differentiated neuroendocrine neoplasms (NENs) are characterized by hyperexpression on the cell membrane of somatostatin receptors (SSTRs). The demonstration of SSTRs, mainly the subtype 2 (SSTR2), is the prerequisite for diagnostic and therapeutic strategies with radiolabeled somatostatin analogs (SSAs). SSTRs can be routinely demonstrated in vivo by SSA-positron emission tomography/computed tomography (SSA-PET/CT) and in vitro by immunohistochemistry (IHC). This systematic review and meta-analysis aimed to gather evidence from the available literature on the correlation between the in vivo PET/CT and in vitro IHC SSTR expression in NEN patients. A systematic review and meta-analysis were conducted following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) 2020 guidelines. A comprehensive literature search was performed in PubMed/MEDLINE and Cochrane Library, selecting studies correlating SSTR expression in NENs via IHC and SSA-PET/CT. Data extraction, quality assessment, and statistical analysis were performed. Eleven studies met the inclusion criteria for systematic review (345 patients). Of these, eight studies (299 patients) provided sufficient quantitative data for meta-analysis. The pooled concordance between SSA-PET/CT and IHC was 76% (95% CI: 67.7–84.2), indicating a good correlation between in vivo and in vitro SSTR2 expression. Heterogeneity among studies was moderate (I2 = 65%), reflecting different patient cohorts and methodologies regarding both SSA-PET/CT and IHC. No significant publication bias was detected. Our results confirmed good agreement between in vivo tumor uptake with SSA-PET/CT and in vitro SSTR2 expression with IHC, highlighting the potential of using IHC for clinical decision-making in NEN patients when SSA-PET/CT is not available.