Stimulation of DNA synthesis by human placental lactogen or insulin in organ cultures of benign human breast tumors.

Twenty biopsy specimens of benign human breast tumors obtained from 20 patients were processed into small slices and individually cultured for 2 days in Medium 199. The medium was supplemented with bovine insulin (5.0 microgram/ml), human placental lactogen (HPL) (10.0 microgram/ml), or ovine prolactin (10.0 microgram/ml). Four hr prior to termination, [3H]thymidine was added to the culture medium to determine DNA synthesis. The addition of insulin to the culture medium consistently increased: (a) the mean incorporation of [3H]thymidine into chemically extracted DNA (p less than 0.05); (b) the mean number of [3H]thymidine-radiolabeled epithelial cells (p less than 0.05), and (c) the mean number of epithelial cells bearing mitotic figures. The addition of HPL increased the mean number of [3H]thymidine-radiolabeled epithelial cells (p less than 0.05) and the mean number of epithelial cells bearing mitotic figures (p less than 0.05). [3H]Thymidine incorporation into chemically extracted DNA was also increased when HPL was added to the medium, although this increase did not quite achieve the 5% level of significance. The addition of ovine prolactin to the culture medium did not have any significant effect on DNA synthesis. This study provides evidence that insulin and HPL are direct stimulants of DNA synthesis of the epithelium contained in benign human breast tumors.