Influence of the antioestrogen tamoxifen on normal breast tissue.

Immunohistochemical assays have been employed to study the expression of ER, PgR, EGFR and Ki67 immunostaining in normal breast tissue (n = 76). The expression of ER and PgR was highly variable in both pre and postmenopausal women and was characterised by large numbers of apparently negative cells. This was most evident for ER-ICA staining in tissues removed from premenopausal women. PgR levels were highest in the ducts of premenopausal women, while EGFR expression was elevated in both ducts and lobules. Ki67 expression was observed in less than 10% of all normal cells and was suppressed by the menopause in lobular tissue. Tamoxifen therapy (40 mg d-1) did not influence the expression of PgR, EGFR or Ki67 immunostaining in cancer associated normal tissue (n = 17). A significant increase, however, was observed in the mean percentage ER positivity in ductal tissue. No effect of duration of tamoxifen therapy was observed on the expression of the antigens studied.