Fertility Preservation Using Tamoxifen and Letrozole in Estrogen Sensitive Tumors Trial

Purpose: Our primary objective is to determine whether concomitant administration of tamoxifen 20 mg oral with gonadotropins (tamoxifen-gonadotropin) versus a starting dose of letrozole 5 mg oral with gonadotropins (letrozole-gonadotropin) will result in a difference in mature oocyte yield during our routine ovarian stimulation protocol for fertility preservation for Estrogen-Receptor-Positive (ER+) breast cancer. Specific Aims: Each of the following aims will include a primary comparison and secondary comparisons. Primary aim: The primary aim will be to compare patients with ER+ breast cancer who are treated with letrozole-gonadotropin versus patients with ER+ breast cancer who are treated tamoxifen-gonadotropin with regard to ovarian stimulation outcomes. * Primary comparison: 1\) To determine if the assigned stimulation regimen will result in a difference in mature (meiosis II) oocyte yield in patients with breast cancer who undergo ovarian stimulation for fertility preservation. * Secondary comparison: 1. To compare estrogen, progesterone, and androgen levels during the ovarian stimulation cycle. 2. To compare estrogen, letrozole, and tamoxifen levels in follicular fluid. 3. To compare duration of stimulation (days) and total gonadotropin dose (international units of FSH). 4. To assess embryo quality, if applicable, on day 3 and day 5 of embryo culture, a measure of the developmental competence of the oocytes. * Experimental comparison: 1. To compare clinical pregnancy rates when cryopreserved tissue is eventually utilized among patients from the assigned stimulation regimens. This comparison is labeled experimental because of the remoteness of such an outcome from our present study. Secondary Aim: We will repeat the above comparisons among patients with ER+ breast cancer who are treated with tamoxifen-gonadotropin versus a prospectively-obtained reference group of patients with Estrogen-Receptor-Negative (ER-) breast cancer who are treated gonadotropin alone. We will then again repeat the above comparisons among patients with ER+ breast cancer who are treated letrozole-gonadotropin versus patients with ER- breast cancer who are treated gonadotropin alone. Experimental Design and Methods: Study population: The target population is reproductive-age women who have been recently diagnosed with ER+ breast cancer and choose to undergo oocyte or embryo cryopreservation prior to chemotherapy treatment. All eligible women will be asked to join the study at their initial University of California, San Francisco (UCSF) fertility preservation consult. Study participants will be recruited from the Reproductive Endocrinology Clinic at University of California, San Francisco Center for Reproductive Health. A consecutive sample with ER- disease will also be recruited at the same type of visit. They will be asked to take part in the gonadotropin only stimulation group, which will be used for a secondary aim.