P-367 Letrozole or Tamoxifen co-administration during fertility preservation of breast cancer patients: a retrospective cohort study

Abstract

Abstract Study question How do fertility preservation (FP) outcomes differ between breast cancer patients stimulated with FSH and Tamoxifen versus FSH and Letrozole? Summary answer Letrozole and Tamoxifen co-administration yielded similar number of retrieved and cryopreserved oocytes/embryos, as well as similar oocyte maturation and fertilization and rates. What is known already Oocyte/embryo cryopreservation is recommended before initiation of chemotherapy in cancer patients. The co-administration of Tamoxifen, a selective estrogen receptor modulator, or Letrozole, an aromatase inhibitor, during ovarian stimulation with gonadotropins, are used to limit the potentially harmful effects of a supra-physiological rise in estrogen levels on hormone-sensitive cancers. However, the optimal choice between the two is still unclear and with no sound evidence. Study design, size, duration Retrospective cohort study of all FP treatments of newly diagnosed breast cancer patients in two tertiary centers between 2000-2022. Collected data included 354 FP cycles of 290 patients and compared treatment parameters and outcomes of Tamoxifen or Letrozole co-administration. Participants/materials, setting, methods Breast cancer patients who underwent FP before chemotherapy were included. Patients with a history of radiation or gonadotoxic treatment, as well as those undergoing other fertility preservation treatments, such as ovarian tissue cryopreservation were excluded. Main results and the role of chance Overall, 215 Letrozole and 139 Tamoxifen treatment cycles were compared, with no significant demographic differences. Treatments with Letrozole had higher FSH dosages (3970IU vs. 2839IU, p < 0.001) but shorter duration (9.7 vs. 10.5 days, p < 0.001). The Letrozole group achieved lower peak E2 levels and endometrial thickness (1508pmol/L, 8.1mm vs. 8760pmol/L, 9.5mm, p < 0.001). The mean number of retrieved oocytes was comparable between the groups (13.6 with Letrozole vs 14.7 with Tamoxifen, p = 0.06). In 122 Letrozole and 46 Tamoxifen patients that underwent strictly oocytes cryopreservation the mean number of cryopreserved oocytes was comparable (11 vs. 12.1, p = 0.21). Moreover, in embryo cryopreservation cycles of 71 patients treated with Letrozole compared to 76 patients with Tamoxifen, no difference was observed in the number of cryopreserved embryos (6.2 vs. 7.0, p = 0.12). Oocyte maturation rate among strictly oocyte preservation cycles was comparable (86% with Letrozole vs. 83% with Tamoxifen, p = 0.80), as were fertilization rates in embryo cryopreservation cycles (62% vs. 63%, p = 0.8 and 71% vs. 76%, p = 0.3 in IVF and ICSI with Letrozole and Tamoxifen, respectively). Multivariate analysis, controlling for potential confounders showed no significant correlations between Tamoxifen or Letrozole co-administration and the number of retrieved oocytes or oocyte maturation rate. Limitations, reasons for caution The primary limitation of our study is its retrospective design and the variation in treatment duration and gonadotrophin dosages among groups. Wider implications of the findings This study provides reassurance that both Tamoxifen and Letrozole are equally effective options when co-administered in FP treatments of breast cancer patients. Trial registration number not applicable