The diagnostic utility of CK5/6 and p63 in fine-needle aspiration of the breast lesions diagnosed as proliferative fibrocystic lesion.

Fine-needle aspiration (FNA) biopsy (FNAB) in the preoperative assessment of breast lesions has shown diagnostic limitations with false-positive and false-negative diagnoses. We investigated the diagnostic value of cytokeratin 5/6 (CK5/6) and p63 in a series of breast FNABs, diagnosed as proliferative breast lesions with or without atypia, to see whether these ancillary studies enhance the ability to make an accurate diagnosis by FNAB. Sixty-four breast FNABs were retrieved between January 2000 and December 2005 and included in the study as follows: 29/64 (45%) cases as proliferative with atypia and 35/64 (55%) without atypia. We also included 10 cases of fibroadenoma. All cases had histological follow-up available for correlation. Immunostaining for CK5/6 and p63 was performed on the cell block material in all cases. The percentage of staining cells in the specimen was graded as 0 (0-10%), 1 (11-25%), 2 (26-50%), and 3 (>50%). There were 9/29 (31%) cases in the atypical group that were found to be malignant on resection, compared with 6/35 (17%) in the cases without atypia. In histologically proven malignant cases, CK5/6 was negative in 11/15 (73%) or showed 1+ stain in 2/15 (13%) cases. In benign breast lesions, CK5/6 stained more than 25% of cell proliferation in 44/49 (90%). p63 showed characteristic staining for single naked bipolar nuclei in the background of the specimen (not appreciated by CK5/6) in all fibroadenoma cases. In conclusion, CK5/6 may enhance the ability to differentiate between benign and malignant epithelial proliferations in breast FNABs. In fibroepithelial lesions, p63 may be more useful than CK5/6.