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Analysis, reporting and interpretation

Stained slides should be scored and interpreted by a qualified pathologist using light microscopy.1,2

Interpretation of controls

A qualified pathologist experienced in IHC procedures must evaluate tissue controls and review the stained product before interpreting results.1,2

Control tissue evaluation criteria (refer to individual product insert, as applicable):1–4

  • Positive control tissue: PD-L1 positive staining, as indicated in product insert
  • Negative reagent control: limited non-specific staining as indicated in product insert
  • Weak to no PD-L1 staining in positive control tissue
  • Excessive non-specific background staining obscuring the identification of PD-L1 positive cells

Tumour-specific IHC examples of high and low PD-L1 expression and negative reagent control


IHC images reproduced with kind permission of MC Rebelatto (NSCLC and HNSCC figures included in Rebelatto MC, et al. Diagn Pathol 2016;11:95; UC image provided by MC Rebelatto).4 Staining appearance between different tests can vary.


Staining results: interpretation

  • Definitions of PD-L1 expression as high/low, as well as tumour cell types used in scoring algorithms, differ among PD-L1 assays.
  • For specific guidance on PD-L1 staining interpretation, please refer to the assay product insert.


  1. VENTANA PD-L1 (SP263) Assay package insert.
    https://www.accessdata.fda.gov/cdrh_docs/pdf16/P160046C.pdf (accessed July 2018).
  2. Dako PD-L1 IHC 28-8 pharmDx package insert.
    http://www.accessdata.fda.gov/cdrh_docs/pdf15/P150025c.pdf (accessed July 2018).
  3. Cree IA, et al. Histopathology 2016;69:177–86.
  4. Rebellato MC, et al. Diagn Pathol 2016;11:95.