Brain metastases of breast and other cancers are increasing in incidence and limiting the gains made by systemic therapy. Here, brain-tropic human metastatic breast cancer cells overexpressing pigment epithelium–derived factor rapidly became apoptotic when implanted into a mouse brain. Red, human mitochondria (tumor cells); green, cleaved caspase-3 stain (apoptosis); blue, DAPI. For details, see the article by Fitzgerald and colleagues on page 144 of this issue.