False-positives in fine-needle aspiration cytology of breast disease can be reduced with p63 immunostaining--a preliminary report.

Myoepithelial cells of the mammary gland are considered to be a key to distinguishing benign from malignant disease in fine-needle aspiration (FNA) cytology. However, identification of these cells with Papanicolaou staining is not easy. The identification of myoepithelial cells was investigated using p63 antibodies to carry out immunostaining of FNA specimens that had been used at the time of Papanicolaou staining for 37 patients who yielded false-positives in FNA. Positively-stained cells were observed in overlying cell clusters or the background in 67.6% of the patients. There is a possibility that over-diagnosis could have been avoided by performing p63 staining for these patients. The controls consisted of stamp samples of fresh specimens obtained from 23 patients at the time of surgery for invasive carcinoma and the results of p63 immunostaining did not reveal any positive staining of tumor cells. Accordingly, these results indicate that there is a strong likelihood that there is no invasive carcinoma when many p63-positive cells are observed in the tumor cell population or the background and that p63 immunostaining has the potential to aid in reducing false-positives at the time of FNA diagnosis of breast disease.