Seemingly counter-intuitive to the essential role of Pfn-1 in cell migration in physiological contexts, invasive and metastatic breast cancer cells present with downregulation of Pfn-1 expression and in fact, Pfn-1 depletion can promote migration and invasion of metastatic human breast cancer cell lines in vitro and escape from the primary tumor in vivo[14]. Here, PFN1 is linked to breast cancer.