DRD1 and breast cancer: We and others have shown that dopamine modulators such as A77636, trifluoperazine, and fluphenazine can reduce the progression of breast cancer via two types of dopamine receptors (DRD1 and DRD2).11–15 Furthermore, we have shown that skeletal loading to the mouse hind limb elevates the urinary level of dopamine.16 Importantly, dopamine does not cross the blood–brain barrier; thus, intravenous administration does not deliver dopamine to the brain.