It is likely that some of the biological pathways activated within the metastatic microenvironment could be non-invasively screened for in blood samples from breast cancer patients as a non-invasive assessment for initiation or growth of a breast cancer liver metastasis; examples of secreted liver factors that were upregulated in response to metastases include NPY, VGF, SCG5, and CXCL1. The gene discussed is NPY; the disease is breast cancer.