Determination of DNA synthesis, estrogen receptors, and carcinoembryonic antigen in isolated cellular subpopulations of human breast cancer

Primary breast adenocarcinomas obtained from ten patients were enzymatically digested using collagenase (1 mg/ml), hyaluronidase (1 mg/ml), elastase (0.1 mg/ml) and DNAse (0.2 mg/ml). The tumor cells were labeled with 3H-thymidine and, in some cases, with 3H-estradiol. The isolated cells were submitted successively to a Ficoll-Hypaque and a bovine serum albumin gradient, from which 12 fractions were obtained. In each fraction, several characteristics were determined: carcinoembryonic antigen (CEA), thymidine (dThd) incorporation, and estrogen receptors (ER). Three main cellular subpopulations were characterized: An intermediate density subpopulation (1.046-1.054 g/ml), in which the proliferating cells are concentrated. In this subpopulation a small number of CEA-positive cells are present, but ER containing cells are virtually absent. A high-density, small cell subpopulation that concentrates most of the ER-containing cells. This subpopulation lacks proliferating cells, but CEA-containing cells are abundant. A low-density subpopulation, lacking proliferating cells and with scarce ER-positive cells, although CEA-positive cells are frequent. These findings strongly suggest that proliferating cells lack ER.