Probably, tumor-related soluble factors [e.g., interleukin (IL)10, indoleamine-pyrrole 2,3-dioxygenase (IDO), prostaglandin E2 (PGE2)] and TME cells are responsible for phenotypic and functional changes in NK cells (Stabile et al., 2017) and help tumors to recruit NK cells. The gene discussed is IDO1; the disease is neoplasm.