Using a three-dimensional (3D) basement membrane matrix (BME or matrigel) culture (also known as MoT (matrigel-on-top) culture: it closely approximates the compliant mechanical microenvironment of lung and mammary gland) that accurately predicts the metastatic outgrowth competency of BCC in the lungs,6,7,15 we show that Pfn1 deficiency causes defects in FLP abundance (a feature of outgrowth-competent cells) and reduces single cell outgrowth ability of TNBC cells. Here, PFN1 is linked to skin basal cell carcinoma.