Special consideration is required when prescribing antipsychotic drugs for patients with an existing diagnosis of breast cancer. The package inserts of all approved antipsychotics contain precautions regarding their administration in this patient group. These drugs are well known to elevate serum prolactin levels to varying degrees. Overexpression of the prolactin receptor is seen in more than 95% of human breast cancers. Many genes that are activated by the prolactin receptor are associated with tumorigenesis and cancer cell proliferation. The authors discuss the pathophysiology, clinical implications, and pertinent preclinical data and make specific recommendations regarding the use of antipsychotics in patients with breast cancer.