ITK and neoplasm: However, a genetic loss of PDCD1, which encodes PD-1, enables a strong expansion of ITK-SYK+ cells and malignant transformation.3 The fact that PDCD1 is often deleted as a tumor suppressor in human T cell lymphomas on the one hand,3 and the clinical relevance of PD-1 as a target for immune checkpoint inhibition or genetic ablation in engineered T cells on the other hand, exemplifies how delicate the T-cell intrinsic balance between oncogenic and tumor suppressor signaling is.