A grand investigation including clinical breast cancer patients, in vivo, ex vivo, and in vitro studies reveals that GPC4 undergoes downregulation in metastatic tumors and that overexpression of GPC4 induces decreased tumorigenicity, i.e., migration and proliferation, in vitro in metastatic cells as well as in vivo in nude mice [23]. Here, GPC4 is linked to breast carcinoma.