PRF1 and neoplasm: Peripheral NK cells from cancer patients as well as tumour-infiltrating NK cells exhibit reduced effector functions such as (i) decreased expression of the membrane protein CD107a, which is a degranulation marker, (ii) decreased secretion of cytokines IFNγ (9, 10) and TNFα (10), and the cytotoxic molecules, perforin (11) and granzyme (12), all of which result in reduced NK cell function against tumour cells.