Using purified NK cells, we found that anti-tumor NK cell functions induced in vitro by IL-2, including direct cytotoxicity, ADCC, and IFNγ secretion, are suppressed by conditioned medium (CM) from neuroblastoma/monocyte co-cultures that contain IL-6 and TGFβ1 and that suppression is removed by the depletion of these cytokines from the CM. Here, IL6 is linked to neoplasm.