Measurement of cellular DNA content as an adjunct to diagnostic cytology in malignant effusions

We reviewed the final diagnosis and outcome of 119 patients who developed serous effusions. In addition to routine cytological examination, the cellular DNA content of fluid samples aspirated from the effusions was measured using flow cytometry in order to determine whether the detection of aneuploid cells could aid in diagnosis or serve as a guide to prognosis. The final diagnosis of 35 patients was non-malignant and a further 40 patients with biopsy-proven cancer had cytologically negative effusions. In all of these cases flow cytometry revealed the presence of diploid cells only. The effusions from 36 cancer patients were reported by cytology to contain a variable proportion of malignant cells, and aneuploid cells were detected in 23 of these samples, the remainder containing only diploid cells. Of 8 effusions where cytology was equivocal, one contained aneuploid cells and clinical outcome subsequently showed that all 8 were malignant. Median survival of patients with cancer was 3 months, and a positive cytology had no influence on survival. However, of the patients with positive cytology, those whose effusions contained aneuploid cells had a poorer short-term prognosis than those cases where only diploid cells could be detected (median survival 1.5 vs 4 months). Measurement of cellular DNA content using flow cytometry can occasionally confirm cancer in a cytologically equivocal effusion, but the negative results in 13 out of 36 (36.1%) effusions where cytology was reported as positive suggests that it has only a limited role in this clinical setting, using currently available techniques.