DNA synthesis in estrogen receptor‐positive human breast cancer takes place preferentially in estrogen receptor‐negative cells

Abstract

The primary breast tumors of 27 patients were analyzed for the expression of estrogen receptors (ER) and DNA synthesis. Seventeen tumors were ER‐positive, and the simultaneous expression of ER and DNA synthesis could be analyzed in 14 ER‐positive tumors. DNA synthesis was measured through the thymidine labeling index (TLI). ER expression was detected by immunohistochemistry with monoclonal antibodies. In these tumors, 38.6% ± 13.1% of the cells were ER‐positive (average TLI = 0.60% ± 0.70%), as opposed to the presence of 61.4% ± 13.1% of ER‐negative cells (average TLI = 0.65% ± 0.53%). In 12 of 14 tumors, both ER‐positive and ER‐negative cells were found to be engaged in DNA synthesis, whereas in two tumors only ER‐negative cells were synthesizing DNA. On the basis of the TLI and the proportion of ER‐negative and ER‐positive cells in the total population, it is suggested that the ER‐positive and ER‐negative compartments are interrelated in most tumors. In five tumors, the ER‐negative compartment would be a precursor of the ER‐positive segment, whereas in six tumors the ER‐positive segment appears to be a precursor of the ER‐negative one. In three tumors, no evidence of an interrelationship between both segments could be found. In the 14 tumors analyzed, it also was found that 69.1% ± 21.3% of the DNA‐synthesizing cells were ER‐negative; this probably accounts for the temporary remissions observed after hormonal treatment in breast cancer. Copyright © 1989 American Cancer Society