Correlation of immunohistopathological expression of somatostatin receptor 2 with standardised uptake values in ⁶⁸Ga-DOTATOC PET/CT

Purpose: In clinical routine somatostatin analogue positron emission tomography/computed tomography (PET/CT) such as ⁶⁸Ga-DOTA-Tyr- octreotide (DOTATOC)-PET/CT could substitute conventional ¹¹¹In- Octreotide scintigraphy. Immunohistochemistry (IHC) for somatostatin receptor 2 (SSTR2) might be a tool to predict positivity of ⁶⁸Ga-DOTATOC in patients where initial staging was not performed, e.g., in incidental findings. We therefore compared a score of SSTR2-IHC with the in vivo standard uptake value (SUV) of preoperative or prebiopsy ⁶⁸Ga-DOTATOC PET/CT. Materials and methods: In 18 patients, ⁶⁸Ga-DOTATOC PET/CT scans were quantified with SUV calculations and correlated to a cell membrane-based SSTR2-IHC score (ranging from 0 to 3). Results: Negative IHC scores were consistent with SUV values below 10. Furthermore, all score 2 and 3 specimens corresponded with high SUV values (above 15). Conclusion: SSTR2-IHC scores correlated well with SUV values and we propose to use SSTR2 immunohistochemistry in patients missing a preoperative PET scan to indicate ⁶⁸Ga- DOTATOC-PET/CT as method for restaging and follow-up in individual patients.