Human triple-negative breast cancer can be treated by modulation of the opioid growth factor (OGF) - OGFr pathway. OGF suppresses cell growth by 20 percent within 24 hours in a receptor-mediated manner. Blockade of OGFr using low dosages of the opioid antagonist naltrexone causes a compensatory increase in OGF and results in 35 percent reductions in cell number within 72 hours. These data demonstrate a novel biological pathway for treatment of this deadly breast cancer.