Microcysts and breast cancer: a study of biological markers in archival biopsy material

Breast cysts are associated with an increased risk of breast cancer. Some biomarkers such as estrogen receptor alpha (ERa), progesterone receptor (PR), and cyclin D1, show similar patterns of expression in epithelial cells lining breast cysts as malignant epithelial cells in local and invasive ductal breast cancer. We have attempted to answer two questions: (1) Do epithelial cells lining breast microcysts (cysts which can only be seen with a microscope) express biomarkers in a similar pattern to breast ductal carcinoma in situ and invasive ductal carcinoma? (2) Are breast microcysts precursors of breast cancer or are they part of normal involution of the breast? Seventy two archival open breast biopsy specimens of ductal carcinoma in situ and invasive ductal carcinoma and 32 normal breast biopsies from Australian women who had breast reduction surgery were selected from hospital archives. All specimens were analysed by standard immunohistochemistry for ERa, PR, cyclin D1, bcl-2, p53 and erbB-2 expression. In the same specimens, the pattern of high biomarker expression was very similar for all the above biomarkers in epithelial cells lining microcysts and in both ductal carcinoma in situ and invasive ductal carcinoma c. ErbB-2 was not expressed in normal control specimens. ErbB-2 was expressed in the same specimens in an increasing proportion of normal breast acini, microcysts and cancer cells in 36% of specimens with breast cancer. An apparent progression was observed from normal breast acini, to proliferation of epithelial cells in microcysts, ductal carcinoma in situ and invasive ductal carcinoma in the same specimen. When these findings are considered with other reports we conclude: (1) that epithelial cells lining breast cysts highly express biomarkers in a similar pattern to ductal carcinoma in situ and invasive ductal carcinoma; (2) that some microcysts are not part of normal involution of the breast and in some women may be part of the transition from normal to cancer.