PRL and breast cancer: The effects of hormone and drug treatments on plasma prolactin (PRL) levels and mammary tumour growth were investigated in rats bearing continuously growing DMBA-induced mammary tumours that responded to bilateral adreno-ovariectomy (Ax + Ox), Oestrogen (E2) administration increased both plasma PRL and tumour growth, but was unable to sustain tumour growth when the PRL level was reduced by concurrent injection of ergocornine (Eg).