PRF1 and colorectal carcinoma: Circulating and tumor-infiltrating NK cells in CRC patients display profound differences in terms of both receptor repertoire and effector functions, showing a drastic reduction in the expression of activating receptors, including NKG2D, NKp30, NKp46, and DNAM-1, as well as in perforin-containing lytic granules [118,119,120,121,122].