title: Is There an Additional Value of Using Somatostatin Receptor Subtype 2a Immunohistochemistry Compared to Somatostatin Receptor Scintigraphy Uptake in Predicting Gastroenteropancreatic Neuroendocrine Tumor Response?
abstract: It is unknown whether tumoral somatostatin receptor subtype 2a (sst2a) immunohistochemistry (IHC) has additional value compared to somatostatin receptor scintigraphy (SRS) uptake using OctreoScan® in predicting response to peptide receptor radiotherapy using 177Lu-octreotate (PRRT) in patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs). The aims of this study were: (1) to establish the percentage of sst2a immunopositivity in GEP-NET samples of PRRT-treated patients, (2) to determine the relationship between best GEP-NET response using RECIST 1.0 criteria 1 year after PRRT and tumoral sst2a IHC, and (3) to compare characteristics of patients with sst2a IHC-negative and -positive tumors.
  
  
  
  All 73 consecutive patients were selected for PRRT based on a positive SRS. Radiological response was scored according to RECIST 1.0 criteria. sst2a status was detected on tumor samples by IHC.
  
  
  
  In total, 93% of GEP-NET samples showed sst2a IHC positivity. No statistically significant relationship was observed between in vitro sst2a expression and in vivo best GEP-NET response 1 year after PRRT (p = 0.47). Sex, primary tumor site, disease stage, ENETS TNM classification, Ki-67 index, highest serum chromogranin-A level, and highest neuron-specific enolase level were not significantly different between patients with negative and positive sst2a tumoral IHC with the exception of age at diagnosis (p = 0.007).
  
  
  
  sst2a IHC of tumor samples has no additional value compared to SRS uptake using OctreoScan® in predicting tumor response after PRRT.
authors.forename: Roxanne C S
authors.initials: RC
authors.lastname: van Adrichem
authors.forename: Kimberly
authors.initials: K
authors.lastname: Kamp
authors.forename: Carolien H M
authors.initials: CH
authors.lastname: van Deurzen
authors.forename: Katharina
authors.initials: K
authors.lastname: Biermann
authors.forename: Richard A
authors.initials: RA
authors.lastname: Feelders
authors.forename: Gaston J H
authors.initials: GJ
authors.lastname: Franssen
authors.forename: Dik J
authors.initials: DJ
authors.lastname: Kwekkeboom
authors.forename: Leo J
authors.initials: LJ
authors.lastname: Hofland
authors.forename: Wouter W
authors.initials: WW
authors.lastname: de Herder
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D007414:Intestinal Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D015282:Octreotide / Q000031:analogs & derivatives* / Q000627:therapeutic use; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D011877:Radionuclide Imaging; D017481:Receptors, Somatostatin / Q000378:metabolism*; D013274:Stomach Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D016896:Treatment Outcome
chemical_list: C554548:177Lu-octreotate; D000970:Antineoplastic Agents; D017481:Receptors, Somatostatin; C574734:SSTR2 protein, human; D015282:Octreotide