PIGF and neoplasm: Tumor-infiltrating NK cells, transformed from CD16+NK to CD16−NK subset upon transforming growth factor-beta (TGF-β) stimulation, predominate in non-small-cell lung carcinoma (NSCLC) and produce elevated levels of pro-angiogenic factors such as VEGF and placenta growth factor (PIGF) to sustain tumor progression (55, 60, 61).