Fig. 5

Sex differences in endothelial cells (ECs), endothelial progenitor cells (EPCs), circulating angiogenic factors, and sex hormones contribute to sex differences in tumor angiogenesis. Female and male ECs express different levels of growth factor receptors, integrins, and cell adhesion molecules, which lead to different abilities to migrate and proliferate, and sex-dependent angiogenic mechanisms. Bone marrow-derived EPCs are more abundant in females, which could be a result of sex hormone regulation. Further, estrogen and androgen facilitate angiogenesis through different mechanisms. Finally, females and males have different amounts of circulating pro-angiogenic and anti-angiogenic factors, which may further contribute to the sex differences in tumor angiogenesis