Expression of TCF1 marker in THRLBCL patients treated with pembrolizumab. Bar chart histograms comparing the percentage of cells positive for TCF1 protein by IHC in r/r THRLBCL treated with pembrolizumab. Patients with clinical benefit after pembrolizumab are indicated in green (CR) and blue (PR); the early nonresponder is depicted in purple. Upper panels: representative areas demonstrating the different content of TCF1 immunohistochemical staining (red) in the 3 samples (Olympus BX53 light microscope, Olympus DP71 camera, original magnification 60×).