Relation between natural killer cells and neoplastic cells in serous fluids

Natural killer (NK) cells are capable of lysing certain tumor cells in vitro. We investigated whether the percentage of NK cells (NK%) in serous effusions has any relation with the presence of malignant cells. Fresh effusions were routinely processed, and a portion of them was submitted for lymphocyte immunophenotyping, using a flow cytometer. Fifty-one fluids (15 peritoneal, 36 pleural), from 47 patients were analyzed. Thirty-two cases were negative and 19 were positive for neoplastic cells: there were 13 adenocarcinomas, 2 malignant mesotheliomas (MM), 3 malignant lymphomas (ML), and 1 rhabdomyosarcoma (R). Negative cases showed an average NK% of 5.09% (1-16%). Effusions positive for adenocarcinoma had an average NK% of 22.08% (12-33%) (P < 0.001). MM, ML, and R had a low NK%, with an average of 3.01% (0-5%). Investigation of the NK% could be useful in cytologically doubtful cases and in the differential diagnosis between MM and adenocarcinoma.