Pfn1 expression is partially downregulated in the primary tumour in human BC, more prominently in those associated with distant metastasis.9,10 In contrast to the pro-migratory role of Pfn in most physiological contexts, there is evidence that downregulation of Pfn isoforms can induce hypermigratory phenotype in certain BCC lines.10–13 At least in MDA-MB-231 (MDA-231: a widely used triple-negative BC (TNBC: ER-, PR-, HER-) cell line) xenograft model, we showed in vivo evidence of increased proficiency of BCC to escape from experimentally established primary tumours upon Pfn1 depletion. The gene discussed is PFN1; the disease is breast cancer.