Growth fractions and estrogen receptors in human breast cancers as determined in situ with monoclonal antibodies.

The growth fraction (GF) and estrogen receptor (ER) status of 76 cases of breast cancer were investigated on frozen sections of the same tissue block by immunostaining with monoclonal antibodies (Ki-67 and anti ER antibody). In 55 cases of this series, the ER status was also determined by standard biochemical methods. Our study revealed an inverse correlation between GF and ER status. This negative relationship was most significant when both variables were determined immunohistologically in the same tissue block and less significant when GF was analyzed by immunohistology and ER status by biochemical methods. These data suggest that the immunohistologically assessed ER values characterize the receptor status of a given carcinoma better than the biochemical values, which leads to the conclusion that the immunohistologically determined close negative relationship between GF and ER reflects the actual in vivo situation of a given breast carcinoma case. However, the immunohistologic analysis also revealed that there is a proportion of exceptional cases, ie, those with a positive ER status and a large or moderately large GF. Because only half of the ER-positive breast carcinomas respond to endocrine therapy with objective remission., it is hypothesized that it might be preferentially these mentioned exceptional cases that fail to positively respond to endocrine treatment protocols.