ThinPrep vs. conventional smear cytologic preparations in analyzing fine-needle aspiration specimens from palpable breast masses

Limited data exist concerning the cellular features of the ThinPrep (Cytyc Corp., Boxborough, MA) technique in the analysis of breast fine-needle aspiration specimens. Therefore, we analyzed a series of 75 surgically excised palpable breast masses and compared ThinPrep and conventional smear fine-needle aspiration preparations. Each mass was aspirated twice. The first sample was used for two alcohol-fixed conventional smears, and the second sample was rinsed into CytoLyt (Cytyc Corp., Boxborough, MA) solution for processing into a ThinPrep slide. The paired slides were separated and independently analyzed for adequacy, overall cellularity, single epithelial cells (absent, rare, moderate, or numerous), epithelial architecture (sheets or three-dimensional clusters), myoepithelial cells and stripped bipolar nuclei (present or absent), and nuclear detail (poor, satisfactory, or excellent). Each sample was classified as negative, negative consistent with fibroadenoma, atypical favoring benign, atypical favoring malignant, or positive for malignant cells. The 75 breast masses included 32 carcinomas and 43 benign lesions. Four conventional smears and one ThinPrep were unsatisfactory. Significantly, more conventional smears were limited by drying artifact (9 vs. 0). ThinPrep aspirates of carcinomas had better nuclear detail (P = 0.03) and greater cellularity (P = 0.05). ThinPrep aspirates of benign masses had greater epithelial cellularity (P = 0.007) and better nuclear detail (P < 0.001), and more specimens had myoepithelial cells (P = 0.007). The ThinPrep interpretation classified 29 of 32 carcinomas (91%) as positive and three as atypical favoring malignant (sensitivity = 100%). The conventional smear interpretation classified 28 of 31 carcinomas (90%) as positive and three as atypical favoring malignant (sensitivity = 100%). The ThinPrep interpretation classified 42 benign lesions as negative (23 cases), negative consistent with fibroadenoma (8 cases), atypical favoring benign (10 cases), and atypical favoring malignant (1 case) (specificity = 74%). The conventional smear interpretation classified 40 benign lesions as negative (25 cases), negative consistent with fibroadenoma (12 cases), and atypical favoring benign (3 cases) (specificity = 93%). ThinPrep was less specific, but the difference was not statistically significant (P = 0.065). In summary, ThinPrep aspirates had greater cellularity and better nuclear detail than conventional smears, and were just as sensitive in identifying the carcinomas. The difference in specificity between the two techniques was not statistically significant (P = 0.065). Diagn. Cytopathol. 1999;21:137-141.