Random-Start Approach in Breast Cancer Patients: Are All Menstrual Cycle Phases the Same?

Abstract – Objectives: The aim of this study was to investigate the ovarian response in different phases of the menstrual cycle in breast cancer women candidates for fertility preservation. Design: A retrospective study was carried out, including women with breast cancer undergoing oocyte cryopreservation at the Fertility Preservation Unit of the University of Naples Federico II between 2017 and 2023. Participants/Materials, Setting, Methods: Women who started ovarian stimulation (OS) during the follicular phase (FP) were compared with those who started during the luteal phase (LP). The two study groups were further stratified according to the phase of the menstrual cycle at OS initiation: early (day 1–5, EFP) or late follicular phase (day 6–14, LFP), early (day 15–21, ELP) or late luteal phase (day 22–32, LLP). The primary outcome was oocyte recovery. Results: A total of 113 women who underwent fertility preservation for breast cancer were included. No differences in oocytes retrieved and ovarian sensitivity were observed when comparing follicular and luteal phases. No differences were observed regarding oocytes retrieved and ovarian sensitivity among the four groups divided according to the menstrual cycle phase. OS was significantly shorter in the early follicular phase (9 days; 8–10) than in the other menstrual phases (LFP: 10 days, 9–11, p < 0.04; ELP: 11, 9–11, p < 0.004; and LLP: 11 days, 10–12, p < 0.001). Limitations: Our study’s limitations are its small sample size and retrospective design. Conclusions: The phases of the menstrual cycle at which OS was started did not affect oocyte yield and ovarian sensitivity in women with breast cancer undergoing a random-start protocol with letrozole.