Estrogen receptor determination in fine needle aspirates of the breast. Correlation with histologic grade and comparison with biochemical analysis.

Material obtained by fine needle aspiration (FNA) of 25 surgically removed breast carcinomas was tested for the immunocytochemical localization of estrogen receptor (ER) using the peroxidase-antiperoxidase method and a monoclonal antibody developed against human breast cancer ER. The results were compared to those obtained by the conventional biochemical analysis of cytosol protein. A semiquantitative relationship between the immunoperoxidase stain and the biochemical analysis suggests that cases in which greater than 70% of the cells stain and in which intense staining is present are likely to contain ER in a concentration of greater than 250 fmol/mg of cytosol. Less than 15% stained cells and an absence of intense staining is indicative of a concentration of less than 10 fmol/mg. In only one case was there a significant difference in positivity between the two methods, possibly as a result of a functional heterogeneity of the tumor cell population. Intense staining is strongly suggestive of a tumor of low histologic grade and was never seen in tumors with a high histologic grade or nuclear grade. The immunoperoxidase method of ER detection on material obtained by FNA is a semiquantitative means of selecting patients with breast cancer who are likely to respond to hormonal therapy. The method overcomes many important disadvantages of cytosol analysis and provides clinically significant information regarding the ER content and the degree of tumor differentiation.