Leukemia/Lymphoma in Cerebrospinal Fluid: Distinguishing Between Cases That Performed Well and Poorly in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytology

Context.—Although the cytologic features of leukemia/ lymphoma in cerebrospinal fluid specimens are well known, the correlation of these features with the ability of cytologists to identify this tumor have not been well studied. Objective.—To identify the morphologic features of leukemia/lymphoma in cerebrospinal fluid that are associated with good performance and poor performance in an educational interlaboratory comparison program; and to identify the morphologic features associated with how well a slide performs with regard to its reference diagnosis. Design.—The performance of 147 cases of leukemia/ lymphoma in the College of American Pathologists Interlaboratory Comparison Program in Non-gynecologic Cytology was analyzed. The cytologic features of a subset of 31 cases composed of relatively equal numbers of Romanowsky-stained and Papanicolaou-stained specimens were further evaluated, and those that performed poorly (n = 12) were compared with those that performed extremely well (n = 19). Results.—For all cases of leukemia/lymphoma in the program, the rate of misclassification as benign for cases with Papanicolaou stain was significantly higher than for those with Romanowsky stain (9.5% vs 2.6%, P < .001). Compared with cases that performed well, slides that performed poorly were more likely to have less than 200 abnormal cells (42% vs 5%, P = .02). The size of the tumor cells and preservation were not significant. Conclusion.—Cases of specimens of leukemia/lymphoma in cerebrospinal fluid are more likely to be misdiagnosed as benign if they are Papanicolaou-stained or have 200 abnormal cells.