Expression of bcl-2-like immunoreactivity in the normal breast and in breast cancer

The expression of bcl-2 protein was analyzed in 336 breast tissue specimens (313 malignant and 23 normal) by immunohistologic staining of frozen and paraffin-fixed tissue. All normal breast specimens and up to 89% of breast carcinoma cases, depending upon the method of tissue fixation, showed positive staining. There was no difference in staining between different tumour types or grades. There was striking heterogeneity of bcl-2-like staining in a large number of specimens of both normal and malignant tissues. In most cases, bcl-2-like protein staining was weaker in normal breast epithelium than in adjacent neoplastic cells suggesting that some tumours overexpress the protein. In normal breast epithelium, myoepithelial cells were negative in the majority of cases. A consistent finding was the absence of any positivity in apocrine metaplasia. The pattern of bcl-2-like staining was not affected by the phase of the menstrual cycle in normal breast biopsies. The bcl-2 protein is known to inhibit programmed cell death and may be important in the expansion of a tumour cell population by contributing to the malignant phenotype of breast cancer.