Formation of new blood vessels (angiogenesis) is important for tumor growth in metastatic breast cancer. It is known that tumors make a protein called vascular endothelial growth factor (VEGF) and there are higher levels of VEGF in the tumors and blood of many women with metastatic breast cancer. VEGF stimulates the formation of blood vessels that supply the tumor with nutrients and oxygen. PTC299 is an oral drug that has been shown to decrease production of VEGF in animal models of human cancer. In these animal models, oral PTC299 administration decreases VEGF levels in the tumor and in the bloodstream, decreases blood vessel numbers in the tumor, and significantly slows or halts tumor growth. Safety studies in research animals indicate good tolerability at doses and drug levels that are higher than those planned for the clinical studies. Results from Phase 1a studies in healthy volunteers indicate that PTC299 achieves levels of PTC299 in the bloodstream that are known to be active in animal models of human cancer. This Phase 1b study is designed to test the hypothesis that PTC299 will be tolerable and will show evidence of VEGF reduction and antitumor activity when administered orally in combination with anastrozole (Arimidex®), letrozole (Femara®), or exemestane (Aromasin®) to women with metastatic breast cancer.