The discrepancy between immunocytochemical and biochemical assay of estrogen receptor in breast cancer patients treated by endocrine therapy.

Estrogen receptor (ER) expression was investigated by ER-immunocytochemical assay (ICA) and the dextran coated charcoal (DCC) method in 10 recurrent or primary-advanced breast cancer patients treated with endocrine or chemo-endocrine therapy. In 6 of these 10 patients, ER was examined both before and after treatments by the 2 methods. ER contents measured by the DCC method were found to be decreased after treatments, however, no change in the immunoreactivities of ER-ICA was observed. In the remaining 4 patients, the ER of new lesions refractory to endocrine or chemo-endocrine therapy was examined. ER status was determined as negative in 3 of the 4 patients by the DCC method, whereas by ER-ICA, the proportion of ER stained cells was about 70 per cent, those cells being diffusely distributed in the section. A discrepancy between ER-ICA and the DCC method was thus demonstrated in breast cancer patients treated by endocrine therapy.