Letrozole or tamoxifen co-administration during fertility preservation for patients affected by breast cancer

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RESEARCH QUESTION: Do fertility preservation outcomes differ between newly diagnosed breast cancer patients stimulated with FSH and tamoxifen compared with FSH and Letrozole? DESIGN: Retrospective cohort study of fertility preservation treatments in newly diagnosed breast cancer patients at two tertiary centres (2000-2022). RESULTS: Patients that underwent 354 fertility preservation cycles participated in the study (n = 290): letrozole (n = 215) and tamoxifen (n = 139). Treatments with letrozole were associated with higher FSH dosages (3970 ± 2027 IU versus 2839 ± 1052 IU, P < 0.001) but were of shorter duration (9.7 versus 10.5 days, P < 0.001). The letrozole group achieved lower peak oestradiol levels (1508 ± 1242 pmol/l versus 8760 ± 5771 pmol/l, P < 0.001) and endometrial thickness (8.1 mm ± 2.4 versus 9.5 ± 2.6 mm, P < 0.001). Mean oocyte number retrieved per cycle was comparable between the groups (13.6 ± 11.7 with letrozole versus 14.7 ± 9.8 with tamoxifen, P = 0.06). In 122 patients taking letrozole and 46 patients taking tamoxifen who underwent strictly oocyte cryopreservation cycles, the mean number of cryopreserved oocytes per cycle was comparable (11 ± 8.4 versus 12.1 ± 7.9, P = 0.21). Similar results were obtained in embryo cryopreservation: letrozole (n = 71 cycles) versus tamoxifen (n = 76 cycles) (6.2 ± 7.1 versus 7.0 ± 5.3, respectively, P = 0.12). Oocyte maturation rates among strictly oocyte preservation cycles were comparable (86 ± 17% with letrozole versus 83 ± 14% with tamoxifen, P = 0.06), as were fertilization rates in embryo cryopreservation cycles (IVF: 62 ± 26% versus 63 ± 26%, P = 0.8; intracytoplasmic sperm injection: 71 ± 28% versus 76 ± 23%, P = 0.30) with letrozole and tamoxifen, respectively. Multivariate analysis, controlling for potential confounders showed no significant correlations between treatment type and the number of retrieved oocytes or maturation rates. CONCLUSION: Letrozole or tamoxifen co-administration with FSH yielded similar number of retrieved and cryopreserved oocytes and embryos, as well as similar oocyte maturation and fertilization rates.

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