Since the induction of VEGF by progestins is well established in breast cancer cells (8,9,21–23,29) and it is possible that one mechanism through which this occurs involves HIF-1α, we undertook studies using both naturally-occurring and synthetic progestins and found that YC-1 inhibits induction of VEGF in both T47-D and BT-474 cells. The gene discussed is HIF1A; the disease is breast cancer.