NPY and breast cancer: For example, substance P (SP), a member of the tachykinin neuropeptide family, is expressed at increased levels in BC cells and BC patient sera, promoting BC cell proliferation and regulating the immune response against BC 200, whereas neuropeptide Y (NPY), a class of highly conserved neuropeptides, also promotes BC cell proliferation and metastasis and is involved in regulation of angiogenesis in BC tissues.