Effect of estrogen on the length of S phase of human breast tissue in organ culture

It is generally accepted that the length of the S phase of the cell cycle, during which DNA replication takes place, is constant in mammalian cells. However, several studies have shown that the hormonal treatment can alter the duration of the S phase, with a consequent increase in DNA synthesis rate. There is very little information regarding the effect of hormones on the S phase of human breast. In the present work normal breast tissue from 38-53 years old patients undergoing surgery for benign lesions was placed in organ culture with and without addition to the culture medium of 17-β-estradiol. After 5 days in culture the length of the S phase was determined by the double labeling technique. The length of S varied from 4.67 to 8.94 hours (6.42 ± 1.9) in the untreated tissue and from 7.41 to 12.10 hours (8.70 ± 1.9) in the hormonally treated breast tissue. Estrogen lengthened the S phase in 5 out of 6 samples with an average percent increment of 41.1%. The differences were significantly different (p < 0.02). It is concluded that there are spontaneous variations in S phase in the human breast epithelium, which could be the result of differences in age or hormonal status of the patient, or variations in cell population among the various compartments of the gland. The lengthening of the S phase under the effect of estrogen indicates that physiologic or non-physiologic hormonal changes can alter the kinetic parameters of the gland modifying the synthesis period of the cell.