Background: Programmed death ligand 1 (PD-L1) score is an important companion diagnosis to predict the response to immunotherapy. Immunohistochemistry can accurately assess the expression of PD-L1 in routine paraffin-embedded tissue. However, whether decalcified or depigmented tissue is still accurate and can be used as a companion diagnosis is controversial. This study attempts to resolve this controversy by analyzing the effects of decalcification and depigmentation at different times on PD-L1 expression.
Methods: Placental tissues were selected for tissue microarray, decalcification was performed according to time gradients of 6, 12, 24, 36, and 48 h, and depigmentation was performed according to time gradients of 1, 5, 15, 30, and 60 min. The intensity of PD-L1 expression at different time points was observed and quantified. Ten PD-L1-positive esophageal squamous carcinoma samples were selected for decalcification treatment, and the PD-L1. Combined Positive Score (CPS), Tumor Proportion Score (TPS) and Immunocyte Proportion Score (IPS) and the positivity rates were compared before and after decalcification.
Results: After the placenta was decalcified, the intensity of PD-L1 positivity diminished, and the average optical density (AOD) value decreased with the prolongation of decalcification time and decreased significantly (P<0.05) at 24 h compared with the control group, and significantly (P<0.01) at 36 and 48 h compared with the control group. The intensity of PD-L1 positivity was weakened considerably after the treatment with potassium permanganate depigmentation. In addition, the AOD value decreased significantly (P<0.01) after the depigmentation time reached 5 min compared with the control group. Ten cases of PD-L1 positive esophageal squamous carcinoma were treated with 24 h decalcification, although the PD-L1 score decreased to a certain degree (P>0.05), and the positivity rate could reach 90%. After 36 h treatment, PD-L1 scores decreased, the CPS and IPS scores decreased significantly (P<0.05), and the positive rate was only 50%.
Conclusions: Potassium permanganate depigmentation significantly reduces PD-L1 expression, even for a shorter time, affecting the accuracy of the results. The accuracy of PD-L1 remained high within 24 h decalcification. The above results have certain reference value for clinical selection of immunotherapy.
Keywords: Programmed death ligand 1 (PD-L1); decalcification; depigmentation; immunohistochemistry.
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