Abstract
Objectives
Immunohistochemistry especially for biomarkers such as PD-L1 in personalized medicine is increasingly being performed on cell blocks from cytopathology samples. We evaluated the effects of staining cell blocks (CBs) from different cytologic fixatives using four different commercially available PD-L1 antibody clones.
Methods
PD-L1 immunohistochemistry (IHC) using four different commercially available clones was performed on eight cell blocks processed from two different fixatives and also on eight formalin-fixed tissues. The clones used were 22C3 at 1:50 dilution and 1:100 dilution, SP263, SP142, and E1L3N. The cell block (CB) samples contained cells that strongly express PD-L1 and either fixed in CytoLyt (methanol-based fixative, n = 4) or CytoRich (ethanol-formalin-based fixative, n = 4). Formalin-fixed control tissues (tonsillar tissue, n = 4; stomach, n = 4) were also included.
Results
Expression for PD-L1 was noted on all the CytoRich fixed cell blocks (n = 4) for all four antibody clones, with the intensity and distribution of expression comparable to the formalin fixed tissues (n = 8). However, consistent absence of expression for PD-L1 was noted on all the CytoLyt fixed cell blocks (n = 4) for all four antibody clones.
Conclusion
The results of this pilot study demonstrate that PD-L1 IHC on cell blocks is feasible. However, there is a need to validate IHC protocols according to specific fixation methods.
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