Effects of insulin, human placental lactogen and human growth hormone of DNA synthesis in organ cultures of benign human breast tumours.

Nineteen benign human breast tumours, from 19 premenopausal patients, were processed into slices and each tumour was individually cultured for 2 days in Medium 199. The effects of bovine insulin (5.0 microgram/ml) human placental lactogen (10.0 microgram/ml) and human growth hormone (10.0 microgram/ml) on 3H-thymidine incorporation into DNA were determined on the cultured tumour slices. Insulin and human placental lactogen significantly (P less than 0.01) increased the mean incorporation of [3H]TdR into DNA, whereas human growth hormone was ineffective. These results provide evidence that insulin and human placental lactogen, but not human growth hormone, may be important factors in the aetiology of benign human breast tumours.