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Characterization of PD-L1 Immunohistochemical Expression in Cell Blocks With Different Specimen Fixation and
Isaac E Lloyd1, Wenhua Zhou2, Benjamin L Witt1
1Department of Pathology and ARUP Laboratories, University of Utah.
Applied Immunohistochemistry & Molecular Morphology : AIMM
|October 31, 2017
Summary
This study shows that cell block preparation methods significantly impact programmed death-ligand 1 (PD-L1) immunohistochemistry (IHC) staining. Cellient automated system blocks offer superior results for PD-L1 IHC interpretation in cytologic specimens.
Area of Science:
- Oncology
- Pathology
- Immunohistochemistry
Background:
- Interpretative criteria for programmed death-ligand 1 (PD-L1) immunohistochemistry (IHC) are primarily based on formalin-fixed, paraffin-embedded tissues.
- Cytologic specimens, particularly cell blocks, are frequently the sole or most accessible tissue for PD-L1 testing.
- Preanalytic variables in cytology sample processing can markedly influence IHC results.
Purpose of the Study:
- To evaluate the impact of common preanalytic variables on PD-L1 IHC staining in cell block preparations.
- To compare different cell block preparation methods and collection media for PD-L1 IHC.
- To assess the feasibility and reliability of PD-L1 IHC interpretation on cytologic specimens.
Main Methods:
- Two cell lines (H441, MCF7) with known PD-L1 expression levels were cultured.
- Cells were collected in various media: PreservCyt, CytoLyt, RPMI, saline, and formalin.
- Cell blocks were prepared using plasma-thromboplastin or Cellient automated systems and stained with the 28-8 PD-L1 antibody.
- PD-L1 expression (intensity, localization) was manually scored by three pathologists across preparation methods.
Main Results:
- Cellient automated system cell blocks demonstrated superior cytomorphology and interobserver agreement.
- Cellient blocks yielded the highest proportion of strong complete membranous PD-L1 staining (82%) with minimal cytoplasmic (11%) and globular (8%) staining.
- RPMI, saline, and formalin samples showed increased cytoplasmic and globular staining; CytoLyt performed poorest overall.
- Observed staining patterns included complete membranous, partial membranous, globular, and cytoplasmic.
Conclusions:
- PD-L1 IHC interpretation on cell blocks is feasible across most examined processing methods.
- Recognition of increased cytoplasmic and globular staining may be necessary for certain sample types.
- Cellient cell blocks provide superior performance for PD-L1 IHC compared to other evaluated methods, enhancing diagnostic reliability.
