A DUAL IMMUNOCYTOCHEMICAL ASSAY FOR ESTROGEN AND EPIDERMAL GROWTH-FACTOR RECEPTORS IN TUMOR-CELL LINES

A new dual immunocytochemical assay for oestrogen receptor (ER) and ep idermal growth factor receptor (EGFR) has been developed. It has been tested in a variety of conditions using cell culture lines and the res ults correlate well with those obtained from single immunocytochemical assays. MCF-7 and A431 cells and a mixture of the two types of cell w ere assessed immunocytochemically for ER and EGFR. ER showed immunopos itivity of 30% in MCF-7 cells, 10% in the mixture and 0% in A451 cells . EGFR demonstrated immunopositivity of O% in MCF-7 cells, 70% in the mixture and 100% in A431 cells. Dual immunocytochemical assays using a nti-ER followed by anti-EGFR monoclonal antibodies on single histologi cal sections showed similar reactivity to the single assays. Three sta ining patterns were seen in the mixture: ER+/EGFR- (MCF-7 cells), ER-/ EGFR- (MCF-7 cells) and ER-/EGFR+ (A431 cells). ZR-75-1 and MDA-MB-231 cells and their retrovirally transfected counterparts ZR/HERc and MDA /HEGO cells were then analysed. The dual assay revealed the fourth phe notype (ER+/EGFR+) in 40% of ZR/HERc cells and in 10% of MDA/HEGO cell s. This is the first description of a dual immunocytochemical assay sy stem for ER and EGFR on single 5 mu m frozen section samples. Studies are now underway assessing breast carcinoma sections which may allow i nvestigation of the clonality of human breast cancer.