Immunohistochemical Demonstration of Cell Proliferation and Estrogen Receptor Status in Human Breast Cancer

Cell proliferation and estrogen receptor (ER) status was investigated in 45 invasive ductal carcinomas of the breast by immunohistochemical methods using monoclonal antibodies Ki-67 (anti-human proliferating cell antibody) and ER-ICA. The results were assessed on the basis of nuclear staining intensity and the percentage of positively stained tumor cell nuclei (index score). There was a significant inverse correlation between the Ki-67 and ER-ICA index scores, although 4 cases showed high index scores for both markers. We conclude that ER-positive cells do not always have low proliferation activity, which may be one of the reasons why endocrine therapy is not effective against all ER-positive breast cancers.