PFN1 and breast cancer: Contrasting these pro-metastatic features associated with LOF of Pfn, we showed that depletion of Pfn1 can severely impair the development of pulmonary metastases from extravasated MDA-231 cells suggesting there may be Pfn1-dependency for metastatic colonisation of TNBC cells.10 However, whether (a) it is the inability to survive or reduced metastatic outgrowth in the lung parenchyma that causes the colonisation defect of BCC upon Pfn1 depletion and (b) there is any potential association between Pfn1 expression and growth-related clinical features in human BC, remain unclear.