Breast cancer is one of the most commonly diagnosed cancers in the US. Metastatic breast cancer has a poor prognosis, and disseminated metastatic breast cancer is the third most frequent cause of cancer related deaths in the US. Many tests for breast cancer subtype have been developed, but none of these provide prognostic information on the risk of metastasis. A method of determining which patients will develop metastatic disease is desperately needed in the field, and better prognostics for metastatic breast cancer would enhance doctors’ ability to tailor treatment plans for each patient. These inventors describe a new prognostic marker for breast cancer metastasis.