A new study has reported that apigenin may inhibit the development of progestin-induced mammary tumors in a rat model of breast cancer. Apigenin is a flavonoid found in a variety of foods, chief among them celery and parsley. Progestin in combination hormone replacement therapy (HRT) has been linked to increased risk of breast cancer. Vascular endothelial growth factor (VEGF) is vital for tumor blood vessel formation. The authors previously demonstrated that medroxyprogesterone acetate, a synthetic progestin used in HRT and birth control pills, increases production of VEGF by tumor cells, resulting in the development of new blood vessels and tumor growth.

In the current study, apigenin was found to significantly delay the development of progestin-accelerated mammary tumors in the rats. Apigenin also reduced the number of mammary tumors. While apigenin delayed the appearance of tumors, it did not block the initial stages of cancer development within the mammary pads. Apigenin was found to reduce progestin-dependent increases in VEGF. On the other hand, estrogen and progesterone receptor levels were not different in the mammary glands of progestin-treated animals, progestin-treated animals administered apigenin, and placebo-treated animals. Nor were there any differences in the number of estrogen receptor positive (ER+) cells. However, the number of progesterone receptor positive (PR+) cells was lower in rats treated with progestin or progestin plus apigenin compared with those treated with a placebo. The authors conclude that apigenin might have important chemopreventive properties for those breast cancers that develop in response to progestins.