Association Between Formalin Fixation Time and Programmed Cell Death Ligand 1 Expression in Patients With Non-Small Cell Lung Cancer.

Background/aim: The expression of programmed cell death ligand 1 (PD-L1) determined by immunohistochemistry (IHC) may be associated with tissue formalin fixation time in non-small cell lung cancer (NSCLC) samples. We investigated the association between the PD-L1 expression and formalin fixation time, and clarified the optimal duration of fixation for accurate PD-L1 evaluation.

Materials And Methods: We collected 55 tumor specimens from resected NSCLC patients. The samples were halved and immediately fixed in 10% buffered formalin for 12-24 h (normal fixation), or 96-120 h (prolonged fixation). Each specimen was stained using two assay systems (22C3 and SP263) for PD-L1.

Results: The mean PD-L1 tumor proportion score was not significantly different between normal and prolonged fixation groups for either 22C3 or SP263 (normal fixation: 18.8%; prolonged fixation: 16.3%, p=0.277; normal fixation: 16.2%; prolonged fixation: 17.6%, p=0.560, respectively).

Conclusion: Formalin fixation duration for up to 120 h does not affect PD-L1 IHC expression. PD-L1 tumor proportion score of tumor specimens can be evaluated by IHC even if these have been fixed in formalin outside the recommended duration in clinical practice.