FLT4 and neoplasm: Increased PPBC tumor sizes, LN positivity, lung micro-metastases, and LYVE1 +mammary lymphatic vessel density 3–4 days after weaning. Increased gene expression of Lyve1, vegfrd, vegfr2, and vegfr3 during involution. Decreased peritumor lymphatic vessel density (60%) and decreased invasion of lymphatics (85%) in shCOX-2 PPBC.