DNA/protein ratio as an index of oestrogen receptor content in human breast cancer

The nuclear DNA/cytoplasmic protein ratio was related to the oestradiol receptor content in both cytoplasmic (ERc) and nuclear (ERn) fractions in 165 cases of breast cancer. The patients under study were divided into groups according to whether their biopsies contained functional (ERc/ERn = +/+), abnormal (+/0) or non-detectable receptor (0/0). The mean microgram DNA/mg protein ratio was significantly decreased in both the abnormal and receptor-negative groups, with means of 30.4 and 30.2 respectively, when compared to the mean of 52.8 for the receptor-positive group. When the DNA/protein ratio for each patient was related to age, a discriminant line which clearly differentiated the ER +/+ group from the other two groups was obtained. It may be concluded that an increased DNA/protein ratio is related to the presence of ERn. Furthermore, since the DNA content per cell is higher in ER-negative tumours, an increase in cellularity must exist in ER-positive tumours.