Ultrastructural identification of neoplastic histiocytes--monocytes: an application of a newly developed cytochemical technique.

We applied a newly developed ultrastructural cytochemical technique utilizing 2-naphthyl thiol acetate (NTA) as a substrate in 3 cases of true histiocytic-monocytic malignancy and 3 controls. The enzyme NTA esterase was identified in both neoplastic and benign histiocytes-monocytes in the form of electron-dense material within the cytoplasm. The NTA esterase varied in size and shape and showed no clear relationship with cytoplasmic organelles. The distribution and pattern of staining were very similar to those of the light-microscopically demonstrated alpha-naphthyl acetate esterase reaction. The main advantages of this method are: 1) histiocytes-monocytes can be identified in the absence of lysosomes or phagocytosis; 2) unequivocal, simultaneous documentation of both histiocytic esterase and subcellular structure is possible; and 3) both blood and solid tissue specimens can be utilized. Our findings demonstrate the usefulness and applicability of ultrastructurally demonstrated NTA esterase in the study of histiocytic-monocytic malignancies.