Diagnostic Reliability of the Acridine Orange Fluorescence Microscope Method for Cytodiagnosis of Cancer*

The cytodiagnostic acridine orange (AO) fluorescence microscope method was applied to exfoliated material from 4348 cases. The method utilizes increased amounts of cytoplasmic ribonucleic acid (RNA) in malignant cells to demonstrate them in brilliant orange and red fluorescence colors. Scanning smears under low magnification readily revealed the presence of cells with increased fluorescence. Usually with higher magnifications it was determined by their morphology whether such cells were cytologically negative, suspicious, or malignant. To test the diagnostic reliability of the fluorescence method, the diagnoses thus reached were compared with those obtained independently by conventional cytodiagnosis on different smears from the same exfoliated specimens. The diagnoses were in agreement with material from the female genital tract, gastric washings, and urine. Some differences in the diagnoses were encountered with exfoliated specimens from the respiratory system. Presumably these were induced by the nature of this material rather than by the method, considering the initially lower reliability of cytodiagnosis with respiratory material in general, and the excellent agreement between fluorescence and conventional diagnoses on most other material. Thus, it is felt that the AO fluorescence method in proper procedure yields as reliable results as do other cytodiagnostic technics; this is in agreement with the findings of other workers who have tested the reliability of the fluorescence method for cytodiagnosis of cancer.