Like many cancers, mammary carcinomas use lymphatic vessels to disseminate, and numerous clinical and experimental studies have documented a strong correlation between peritumoral lymphangiogenesis and tumor dissemination. At the same time, many other factors can affect the incidence, invasiveness, and mortality of breast cancer, including lactation history. Although lactation reduces overall cancer risk, patients diagnosed within 5 years of pregnancy have an increased incidence of metastatic disease. In this issue of the JCI, Lyons and colleagues demonstrate that postpartum breast tissue remodeling during involution coincides with inflammatory lymphangiogenesis. In mouse models, cyclooxygenase-2 (COX-2) inhibition during involution reduced the risk of cancer metastasis and correlated with decreased lymphangiogenesis. In addition to lymphangiogenesis, COX-2 inhibition reduces many of the immune-suppressive features of the tumor microenvironment, including development of myeloid-derived suppressor cells and regulatory T cells; therefore, these results support the notion that inhibiting COX-2 during lactation weaning may lessen the incidence of breast cancer metastasis.