Diagnostic significance of the immunoexpression of CD34 and smooth muscle cell actin in benign and malignant tumors of the breast.

PURPOSE: Our aim was to investigate the distribution of CD34 and smooth muscle cell actin positive myofibroblasts in the stroma of the normal mammary gland, benign and malignant tumors. The observations were especially focused on the diagnostic value of the cumulative results obtained with these immunoreactions.
METHODS: Our study included 112 female patients with suspect breast masses obtained by surgery or biopsy. We performed morphological study and immunohistochemistry for CD34 and SMA.
RESULTS: We have found normal breast tissue, sclerosing adenosis, fibroadenomas, fibrocystic diseases, phyllodes tumor, DCIS, ductal invasive, lobular, squamous, medullary, mucinous, and papillary carcinomas. We also found apocrine metaplasia, florid ductal hyperplasia, atypical hyperplasia, papilloma and LCIS associated with the malignant tumors. All the normal breast tissues and most of benign lesions were positive for CD34 and negative for SMA. The exceptions were represented by a case of fibroadenoma and the phyllodes tumor, with CD34 positivity and a focal acquisition of SMA; fibrocystic disease with associated apocrine metaplasia adjacent to a squamous carcinoma with loss of CD34 expression and focal acquisition of SMA. All our DCIS and invasive carcinomas have lost CD34 expression and gained SMA positivity. Some particular behavior had the mucinous and squamous carcinomas.
CONCLUSIONS: Although there were some exceptions especially when one of the two markers was interpreted separately and in some cases associated with sclerotic stroma, we conclude that the combined expression of CD34 and a-SMA is of potential diagnostic value in the distinction between benign and malignant tumors in some difficult cases.