What constitutes an adequate smear in fine-needle aspiration cytology of the breast?

BACKGROUND: The false-negative diagnosis is a major clinical concern and a significant cause of litigation in fine-needle aspiration cytology of breast lesions. A significant number of false-negative diagnoses may be due to inadequate sampling of these lesions. Little information is available in the literature about what constitutes an adequate specimen, and the few publications that address this issue propose criteria based on anecdotal information. Recommendations vary widely and may or may not take clinical findings into account. METHODS: The authors studied a subgroup of 183 cases with known outcome, drawn from a series of 1779 cases, to determine the minimum number of cell clusters necessary to ensure that adequate cellular material was present for accurate diagnosis. The series included 21 cases cytologically diagnosed as false-negative, 75 cases that had been correctly identified as benign, 47 cases cytologically designated as atypical, and 40 cases that on initial review had been correctly identified as malignant. In semiblind fashion, the smears from each case were assigned to low, medium, and high cellularity categories. Low cellularity was defined as 10 or fewer cell clusters, moderate cellularity was defined as 11-30 clusters, and high cellularity was defined as more than 30 clusters. A cell cluster was defined as five or more cells. Within the low cellularity group, exact numbers of cell clusters and the presence of individual cells were recorded. The presence of bipolar cells was used as an adjunct criterion for specimen adequacy, and the bipolar cells in each of 10 x 200 fields were counted. Cellularity was then correlated with diagnostic accuracy. RESULTS: Using a cutpoint of a cumulative score of 6 or more cell clusters or the prominence of bipolar cells (> or = 10 in each of 10 medium-power, x200 fields) for assessment of specimen adequacy, a false-negative rate of 1.5%, associated with an unsatisfactory rate of 20.2%, was obtained. CONCLUSIONS: Based on the data gathered in this study, the authors believe that the sampling false-negative and unsatisfactory rates can be minimized by selecting a cutpoint for satisfactory smears at a level of 6 or more cell clusters (cumulative total) or the presence > or = 10 intact bipolar cells per 10 medium-power fields (x200). Use of these criteria will decrease the false-negative rate of sampling in epithelial lesions of the breast. A false-negative rate of approximately 1.5% was obtained in association with an unsatisfactory rate of 20.2%. Using a cutpoint of 1 or more cell clusters, a false-negative rate of 2.1%, associated with an unsatisfactory rate of 13.7%, was obtained.