High Expression of TIM 3 and Galectin 9 on Immunohistochemistry Staining of Tumor Specimen at Diagnosis in Pediatric Patients with Ewing Sarcoma.

Significant progress has been made in the advancement of immune system modulation for cancer treatment in recent years. In particular, immune checkpoint inhibitors and chimeric antigen receptor (CAR) T-cell therapy have demonstrated remarkable clinical benefit in relapsed/refractory cancers. However, our understanding of the immuno-oncologic landscape in pediatric solid tumors remains limited and is a barrier to continued progress. We examined the immunohistochemical expression of checkpoint receptors PD-1, TIM-3, LAG-3 and their respective ligands in various pediatric cancers at diagnosis and found high expression of TIM-3/Galectin-9 in the infiltrating cells of Ewing sarcoma. Location of checkpoint receptor/ligand expressions is important, as some staining patterns were only seen along tumor borders. Finally, peripheral T cell function varied significantly among different tumors supporting a complex relationship between the tumor microenvironment and the global immune system.