The gene for predicting whether breast cancer will spread has been found. This can be key in designing medications that can help stop cancer metastasis:

Researchers have identified a set of genes that seems to predict if breast cancer will spread to the lungs and how serious the disease will be.

The finding could eventually help doctors to predict whose disease will become aggressive and spread, and potentially help them to better target treatments. The lungs and the bones are frequent sites for cancer that spreads from the breast. And cancer that spreads from the breast to organs such as the lungs accounts for the majority of breast cancer-related deaths, research has shown.

(Doheny, "Genes Discovered That May Predict Breast Cancer Spread to Lungs", Forbes, Jul.27)