Usefulness of immunocytochemistry using a Breast Marker antibody cocktail targeting P63/cytokeratin7/18/cytokeratin5/14 for fine needle aspiration of the breast: a retrospective cohort study of 139 cases.

OBJECTIVE: The Breast Marker Cocktail from Biocare Medical comprises five antibodies recognising p63, and cytokeratins (CKs) 7, 18, 5 and 14. Immunohistochemistry using this cocktail is useful for diagnosing proliferative intraductal breast lesions. However, cytology using the cocktail has not been reported. METHODS: We report 139 cases of mammary samples collected by fine needle aspiration (FNA) for which histological diagnoses were available. After cell transfer, immunocytochemistry was performed using the cocktail, and clusters of cells were classified. A cluster with no or limited CK5/14 expression (<20% of cells) was classified as a monotonous cluster. One with more than 20% of cells showing CK5/14 expression was defined as a mosaic cluster. When at least one p63-positive cell was present, we defined it as a cluster with p63. We also evaluated background p63-positive myoepithelial cell densities. RESULTS: The diagnostic sensitivity and specificity for carcinomas were 97.8% (89/91) and 91.7% (11/12), respectively, using the criterion of two or more monotonous clusters lacking p63. Two false-negative cases were triple-negative cancers; one false-positive was an apocrine papilloma. The numbers of monotonous clusters with p63 differed significantly between benign lesions, ductal carcinoma in situ (DCIS)/lobular carcinoma in situ (LCIS) and invasive carcinomas (P < 0.001). The background myoepithelial cell density was significantly higher in fibroepithelial tumours than in other lesions (P < 0.001). CONCLUSIONS: Immunocytochemistry using this antibody cocktail showed good sensitivity and specificity for diagnosing breast cancers. Thus, this method is useful for mammary cytology using FNA.