Expression of immune checkpoint receptors Indoleamine 2,3‐dioxygenase and T cell Ig and ITIM domain in metastatic versus nonmetastatic choroidal melanoma

Abstract Background Survival in metastasized cutaneous melanoma (CM) has been improved with the advent of inhibitors of immune checkpoints CTLA4 and PD‐1. In contrast, the response rate for inhibition of these checkpoints in uveal melanoma (UM) is very low. Other checkpoints including IDO and TIGIT may be targetable. Methods Sections from 6 patients with UM, who had undergone primary enucleation 1978—1995 and 6 paired liver metastases were stained immunohistochemically (SOX10, Melan‐A, IDO, TIGIT, and CD8). Four tumors from patients who did not develop metastasis during a mean follow‐up of 19 years, and 5 samples each of normal choroidal and liver tissue were included for comparison. The number of cells/mm2 expressing IDO, TIGIT and CD8 was counted with manual and digital image analysis methods. Retrospective data on patient and tumor characteristics was reviewed. Results The number of TIGIT positive cells was significantly higher in primary tumors from patients who eventually developed metastases (mean 4695 cells/mm2) than from patients who didn't (mean 1342 cells/mm2, P