 During standard ovulation stimulation, the estrogen levels will exceed normal levels and may reach 10 times the normal level for a 2 week period. This may not be desirable in breast cancer patients. The study hopes to determine if the investigators can stimulate oocyte development in the conventional way and administer different doses of Letrozole as the oocytes develop, to keep estradiol levels low, increase the number of oocytes the investigators are able to recover, and improve the quality of those oocytes. 