Cancer growth and spread are saltatory and phase-locked to the reproductive cycle through mediators of angiogenesis.

The frequency of breast cancer metastatic spread is affected by the menstrual cycle phase of its resection. Breast cancer growth, post-resection spread, and cure frequency are each modulated by the estrous cycle in C(3)HeB/FeJ mice. Tumor metastases are 2- to 3-fold more frequent when the resection is done during diestrus as compared with estrus. Tumor angiogenesis is essential for both cancer growth and lethal metastatic cancer spread. The balance between vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) modulates new blood vessel formation and blood vessel permeability. Sex hormones modulate the expression of these key angiogenesis regulators in the endometrium and uterus. We, therefore, asked whether the estrous cycle modulates the density of CD31-positive vessels within the tumor, the permeability of tumor blood vessels, levels of VEGF and bFGF immunoreactive protein in normal breast and breast cancer, and whether expression of these genes are modulated by the estrous cycle stage in C(3)HeB/FeJ mice. We find that tumor blood vessel density and blood volume do not vary throughout the cycle; however, tumor capillary permeability is regulated by the estrous cycle being highest in diestrus, the cycle stage associated with the highest cancer growth rate and the highest frequency of post-resection cancer metastasis. VEGF protein levels in breast cancer are >100-fold higher than in normal breast. VEGF protein in this mammary tumor varies with the estrus cycle with highest levels in proestrus. In a non-breast tumor, methylcholantrenene A sarcoma, from CD(2)F(1) mice, tumor VEGF protein also varies with the estrus cycle with highest levels in proestrus and diestrus. VEGF gene expression in the mammary tumor does not change significantly across the cycle, but is modulated by the cycle in normal breast tissue. bFGF protein concentration is 6-fold higher in normal breast than in breast cancer. bFGF protein pattern in both tumor and breast are similar, opposite to VEGF, and affected by oophorectomy. bFGF message is modulated by the cycle in both breast cancer and normal breast. The changes in breast cancer capillary permeability, VEGF, and bFGF that occur during each fertility cycle, in breast tissue and breast cancer, putatively in response to cyclical changes in sex hormones, might contribute, at least in part, to both the modulation of cancer growth and post-resection breast cancer spread by the fertility cycle. These fertility cycle-induced effects on tumor biology also seem to extend to non-breast cancer biology.