FLT4 and lobular neoplasia: Importantly, blocking the feedforward loop‐induced VEGF‐C/VEGFR3 signaling with its specific inhibitor SAR131675 inhibited exosomal BCYRN1‐mediated LN metastasis in vivo, suggesting that the formation of this loop functions as a detector to enable the rapid and effective response for the activation of VEGF‐C/VEGFR3 signaling and supports the promotion of BCa LN metastasis.