STAT3 and neoplasm: In this study, we investigated the role APN on CD8+ T cells in the tumor microenvironment of rhabdomyosarcoma-bearing mice, and found that APN deficiency inhibited rhabdomyosarcoma growth, which was associated with enhancing the anti-tumor response of CD8+ T cells that infiltrated rhabdomyosarcoma through the inhibition of STAT3 activation.