title: Expression of somatostatin receptors 2 and 5 in circulating tumour cells from patients with neuroendocrine tumours.
abstract: BACKGROUND
  Neuroendocrine tumours (NET) overexpress somatostatin receptors (SSTR) that can be targeted for therapy. Somatostatin receptor expression is routinely measured by molecular imaging but the resolution is insufficient to define heterogeneity. We hypothesised that SSTR expression could be measured on circulating tumour cells (CTCs) and used to investigate heterogeneity of expression and track changes during therapy.
  
  
  METHODS
  MCF-7 cells were transfected with SSTR2 or 5 and spiked into donor blood for analysis by CellSearch. Optimum anti-SSTR antibody concentration and exposure time were determined, and flow cytometry was used to evaluate assay sensitivity. For clinical evaluation, blood was analysed by CellSearch, and SSTR2/5 immunohistochemistry was performed on matched tissue samples.
  
  
  RESULTS
  Flow cytometry confirmed CellSearch was sensitive and that detection of SSTR was unaffected by the presence of somatostatin analogue up to a concentration of 100 ng ml-l. Thirty-one NET patients were recruited: grade; G1 (29%), G2 (45%), G3 (13%), primary site; midgut (58%), pancreatic (39%). Overall, 87% had SSTR-positive tumours according to somatostatin receptor scintigraphy or 68-Ga-DOTATE PET/CT. Circulating tumour cells were detected in 21 out of 31 patients (68%), of which 33% had evidence of heterogeneous expression of either SSTR2 (n=5) or SSTR5 (n=2).
  
  
  CONCLUSIONS
  Somatostatin receptors 2 and 5 are detectable on CTCs from NET patients and may be a useful biomarker for evaluating SSTR-targeted therapies and this is being prospectively evaluated in the Phase IV CALMNET trial (NCT02075606).
authors.affiliation: UCL Cancer Institute, University College London, London WC1E 6DD, UK.
authors.forename: Alexa
authors.initials: A
authors.lastname: Childs
authors.affiliation: UCL Cancer Institute, University College London, London WC1E 6DD, UK.
authors.forename: Clare
authors.initials: C
authors.lastname: Vesely
authors.affiliation: UCL Cancer Institute, University College London, London WC1E 6DD, UK.
authors.forename: Leah
authors.initials: L
authors.lastname: Ensell
authors.affiliation: UCL Cancer Institute, University College London, London WC1E 6DD, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Lowe
authors.affiliation: Department of Histopathology, Royal Free London NHS Foundation Trust, London NW3 2QG, UK.
authors.forename: Tu Vinh
authors.initials: TV
authors.lastname: Luong
authors.affiliation: Department of Gastroenterology, Royal Free London NHS Foundation Trust, London NW3 2QG, UK.
authors.forename: Martyn E
authors.initials: ME
authors.lastname: Caplin
authors.affiliation: Department of Gastroenterology, Royal Free London NHS Foundation Trust, London NW3 2QG, UK.
authors.forename: Christos
authors.initials: C
authors.lastname: Toumpanakis
authors.affiliation: UCL Cancer Institute, University College London, London WC1E 6DD, UK.|Department of Oncology, Royal Free London NHS Foundation Trust, London NW3 2QG, UK.
authors.forename: Christina
authors.initials: C
authors.lastname: Thirlwell
authors.affiliation: UCL Cancer Institute, University College London, London WC1E 6DD, UK.
authors.forename: John A
authors.initials: JA
authors.lastname: Hartley
authors.affiliation: UCL Cancer Institute, University College London, London WC1E 6DD, UK.|Department of Oncology, Royal Free London NHS Foundation Trust, London NW3 2QG, UK.
authors.forename: Tim
authors.initials: T
authors.lastname: Meyer
mesh_terms: D006801:Humans; D018358:Neuroendocrine Tumors / Q000097:blood*; D017481:Receptors, Somatostatin / Q000097:blood*
chemical_list: D017481:Receptors, Somatostatin; C094573:somatostatin receptor 5; C093733:somatostatin receptor 2