Human breast cancer and impaired NK cell function.

Recent advances in tumor immunology have led to the discovery of a new lymphoid cell with unique antitumor activity. Natural killer (NK) cells form an antitumor surveillance system and appear to be vital in preventing tumor growth and metastasis in animal models. We studied NK activity in patients with benign and malignant breast disease, using a chromium-51 release microtiter cytotoxicity assay with K562 cells as targets. Compared with benign controls, patients with malignancies had significantly depressed NK-mediated lysis (P less than 0.01). Furthermore, lysis in those with advanced disease (stages II, III, and IV) was significantly less than in those with limited disease (stage I) (P less than 0.01). NK activity was not correlated to estrogen or progesterone receptor states. Positive correlation of a depressed natural killer activity with the extent of tumor spread supports the concept of an NK cell immune surveillance system in breast cancer and emphasizes its importance in this malignancy.