CD57 antibody [NK-1] marks a subset of lymphocytes known as natural killer (NK) cells. Follicular center cell lymphomas often contain many NK cells within the neoplastic follicles. Studies have shown that CD57 expression is present in normal and neoplastic pituitaries. It has been reported that CD57 reactivity may be used as an additional immunophenotypic criterion in distinguishing nodular lymphocyte predominance Hodgkin’s disease from nodular sclerosing Hodgkin’s disease, T-cell-rich B-cell lymphoma, and follicular lymphoma. CD57 [NK-1] also reportedly stains neuroendocrine cells and their respective tumors.