Fig. 1.

Immunohistochemical labeling of metastatic melanoma primary lesions or metastases. a All tumour (melanoma) cells are programmed death–ligand-1 (PD-L1)–positive, which is quite rare (×100, E1L3N clone). b A sample with >5% PD-L1–positive tumour area. Note: the disposition of the PDL1+ cells at the tumour edge is very common (×100, E1L3N clone). c SOX10 (purple nuclei) and PDL1 (brown membranes) double-labeling. Note: PD-L1+ is expressed both by immune cells (SOX10 negative, red triangle) and tumour melanocytes (SOX10 positive, red star) (×200). d SOX10 (purple nuclei, red arrow) and CD163 (brown membranes, red star) doublelabeling. Note: CD163-labeling of histiocyte cytoplasmic extensions surrounding SOX10+ tumour cells could suggest that some PD-L1+ cells thought to be tumoural might rather be PD-L1– tumour cells surrounded by positive histiocyte cytoplasmic extensions (×200)