9026 Background: ASCO recommends that young cancer patients be referred to specialists for fertility preservation (FP) as soon as possible after the diagnosis, however, there is no data to directly support that recommendation. The purpose of this study was to determine if early referral improves FP outcomes in young women with breast cancer undergoing adjuvant chemotherapy and/or radiotherapy. Methods: We performed a secondary analysis of a prospective database (Controlled Ovarian Stimulation Treatment with Letrozole Supplementation Study, COST-LESS, JCO 2009) of 154 women with breast cancer undergoing ovarian stimulation (OS) for FP by embryo or oocyte cryopreservation. Complete data were available in 93 patients with mean age of 35.2±4.4 years (range: 24 to 44). Results: Thirty-six of the 93 patients were referred and evaluated prior to breast surgery (PreS) and 57 post-surgery (PostS). PreS and PostS groups were similar in terms of age, cancer stage, and receptor or BRCA status. Likewise the mean number of oocytes or embryos cryopreserved per cycle were similar between the two groups. The time period from the first diagnosis date (FD) to initiation of OS was significantly shorter in patients who were referred PreS vs. PostS (43.0±28.0 vs. 72.5±30.6 days, p<0.001, Mann Whitney U test). There was, however, no difference in the length of time from FD to surgery date and from the date of first FP consultation to initiation of OS between the two groups. Six of 36 patients in the PreS group and 1 of 57 in the PostS group were able to undergo two FP cycles (p = 0.012, Fisher's exact test). This resulted in an additional 79 vs. 5 oocytes obtained in PreS vs PostS groups respectively. Patients who underwent first oocyte retrieval within 5 weeks of the surgery were able to complete a second cycle within 9 weeks of the surgery. Conclusions: Early referral prior to breast cancer surgery enables multiple cycles of FP without a delay in chemotherapy beyond 9 weeks post surgery. Women who can undergo multiple cycles may be at an advantage for FP because of additional number of eggs/embryos cryopreserved. This is the first study demonstrating the benefit of early FP referral in cancer patients. Practitioners should adhere to FP guidelines issued by ASCO in 2006. No significant financial relationships to disclose.