PDCD1 and cancer: In addition to the well-established role of PD1 in dampening T-cell responses,10,15 recent evidence suggests that the PD1 receptor also is expressed by cancer cell subsets16 and that tumor cell-intrinsic PD1 pathway activation promotes cancer progression by triggering tumor cell-intrinsic growth pathways, including PI3K/AKT/mTOR.16–18