Impact of delayed fixation and decalcification on PD-L1 expression: a comparison of two clones.

The bone is a frequent localization for lung non-small cell cancer metastasis; decalcification is required to permit tissue section. Pre-analytical conditions can influence the detection of immunohistochemical markers. The aim of our work is to evaluate PD-L1 expression in samples with delayed fixation and in decalcified tissue with chelating agent or acid at different time. Tumor-expressing PD-L1 and placental tissue were fixed at different times or decalcified with an acid decalcifier or EDTA for different durations. For 22C3 antibody, when tissues were decalcified with DC3, there was a significant decrease in the percentage of tumor cells or placental villi stained which after 4 h (p = 0.035 at 4 h). When EDTA is used for 22C3 antibody, there was a slight decrease in the percentage of stained tumor cells or villi but although there was a trend (p = 0.058 at 20 h), this was never statistically significant. For E1L3N antibody, when tissues were decalcified either with DC3 or EDTA, there was no significant decrease for the proportion of stained tumor cells or placental villi, neither for staining intensity for the first 24 h. The proportion of placental villi and tumor stained or intensity of staining was not significantly lower for any sample after delayed fixation also at 24 h for both PD-L1 clones. Delayed fixation does not affect the proportion of stained cell and intensity with PD-L1 immunohistochemistry. Decalcification also performed with EDTA lower the proportion and intensity of stained cells with PD-L1 immunohistochemistry.