ABSTRACT
<p><b>OBJECTIVE</b>To assess the clinicopathological features of atypical cystic duct (ACD) as a precancerous lesion of the breast.</p><p><b>METHODS</b>Whole mammary gland serial sections were performed on 200 cases of breast cancer without pre-operative biopsy (prior operation, fine needle aspiration or needle biopsy were routinely performed in each case). The clinicopathological findings and immunohistochemical features of ACD were investigated.</p><p><b>RESULTS</b>Forty-four (22%) of the 200 breast cancer patients had ACD breast lesions. The frequency of patients with ACD increased in premenopausal women (P=0.001). A number of ACD lesions displayed a histological transition to adjacent ductal carcinoma in-situ. In 16 of 44 (36%) patients with ACD, carcinoma cells stained positive for p53. In 12 of these 16 cases (75%), ACD cells also stained positive for p53 protein (P=0.001). Myoepithelial cells of ACD appeared attenuated and stained strongly for alpha-smooth muscle actin. There was no correlation between the ACD-present group and the ACD-absent group in tumor size, nodal metastasis, and immunostaining patterns of estrogen receptor (ER), progesterone receptor (PR), p53, c-erbB-2 and Ki-67 labeling index of cancerous tissues. All 44 ACD lesions showed a negative staining of c-erbB-2, regardless of the staining result in their corresponding carcinomas. The mean Ki-67 labeling index of ACD lesions was low.</p><p><b>CONCLUSIONS</b>ACD is frequently associated with breast cancer. It may represent a precancerous mammary lesion, supported by the frequent histological continuum between ACD and malignancy, and simultaneous p53 over-expression present in both ACD and its corresponding breast carcinoma.</p>