title: Intra-image referencing for simplified assessment of HER2-expression in breast cancer metastases using the Affibody molecule ABY-025 with PET and SPECT.
abstract: OBJECTIVE
  In phase I/II-studies radiolabelled ABY-025 Affibody molecules identified human epidermal growth factor receptor 2 (HER2) expression in breast cancer metastases using PET and SPECT imaging. Here, we wanted to investigate the utility of a simple intra-image normalization using tumour-to-reference tissue-ratio (T/R) as a HER2 status discrimination strategy to overcome potential issues related to cross-calibration of scanning devices.
  
  
  METHODS
  Twenty-three women with pre-diagnosed HER2-positive/negative metastasized breast cancer were scanned with [111In]-ABY-025 SPECT/CT (n = 7) or [68Ga]-ABY-025 PET/CT (n = 16). Uptake was measured in all metastases and in normal spleen, lung, liver, muscle, and blood pool. Normal tissue uptake variation and T/R-ratios were established for various time points and for two different doses of injected peptide from a total of 94 whole-body image acquisitions. Immunohistochemistry (IHC) was used to verify HER2 expression in 28 biopsied metastases. T/R-ratios were compared to IHC findings to establish the best reference tissue for each modality and each imaging time-point. The impact of shed HER2 in serum was investigated.
  
  
  RESULTS
  Spleen was the best reference tissue across modalities, followed by blood pool and lung. Spleen-T/R was highly correlated to PET SUV in metastases after 2 h (r = 0.96, P < 0.001) and reached an accuracy of 100% for discriminating IHC HER2-positive and negative metastases at 4 h (PET) and 24 h (SPECT) after injection. In a single case, shed HER2 resulted in intense tracer retention in blood. In the remaining patients shed HER2 was elevated, but without significant impact on ABY-025 biodistribution.
  
  
  CONCLUSIONS
  T/R-ratios using spleen as reference tissue accurately quantify HER2 expression with radiolabelled ABY-025 imaging in breast cancer metastases with SPECT and PET. Tracer binding to shed HER2 in serum might affect quantification in the extreme case.
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. dan.sandberg@igp.uu.se.
authors.forename: Dan
authors.identifier: http://orcid.org/0000-0002-0058-278X
authors.initials: D
authors.lastname: Sandberg
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
authors.affiliation: Section of Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.
authors.forename: Irina
authors.initials: I
authors.lastname: Velikyan
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Helena
authors.initials: H
authors.lastname: Olofsson
authors.affiliation: Affibody AB, Solna, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Wennborg
authors.affiliation: Affibody AB, Solna, Sweden.
authors.forename: Joachim
authors.initials: J
authors.lastname: Feldwisch
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Jörgen
authors.initials: J
authors.lastname: Carlsson
authors.affiliation: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Lindman
authors.affiliation: Section of Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.
authors.forename: Jens
authors.initials: J
authors.lastname: Sörensen
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000097:blood / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology*; D019788:Fluorodeoxyglucose F18; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008875:Middle Aged; D009362:Neoplasm Metastasis; D010446:Peptide Fragments / Q000493:pharmacokinetics; D000072078:Positron Emission Tomography Computed Tomography; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000097:blood / Q000378:metabolism*; D013205:Staphylococcal Protein A; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D019788:Fluorodeoxyglucose F18; D010446:Peptide Fragments; D018719:Erb-b2 Receptor Tyrosine Kinases; D013205:Staphylococcal Protein A; C549680:ABY-025; C508053:ERBB2 protein, human
keywords: Affibody; HER2-receptor; PET; SPECT; Shedding; T/R