Ovaries of patients recently treated with alkylating agent chemotherapy indicate the presence of acute follicle activation, elucidating its role among other proposed mechanisms of follicle loss

Objective: To investigate mechanisms of primordial follicle (PMF) loss in vivo in human ovaries shortly after alkylating agent (AA) chemotherapy. Design: Cohort study. Setting: Tertiary university medical center. Patient(s): Ninety-six women aged 15–39 years who underwent ovarian tissue cryopreservation for fertility preservation. Intervention(s): Fresh ovarian tissue samples were harvested from women treated with AA (n = 24) or non-AA (n = 24) chemotherapy <6 months after treatment and age-matched untreated women (n = 48). Main Outcome Measure(s): Differential follicle counts, time from chemotherapy exposure, immunostaining for apoptosis (cleaved caspase-3) and FOXO3A on tissue harvested within ultrashort time intervals (4–12 days), collagen (Sirius red) and neovascularization (CD34). Result(s): AA-treated ovaries had significant loss of PMFs, and significant increase in absolute numbers of growing follicles compared with untreated control ovaries. The number of growing follicles was inversely correlated with time from chemotherapy. Representative staining for FOXO3A observed decreased nuclear localization in PMF oocytes in AA-treated ovaries removed within the ultrashort time interval compared with untreated ovaries. Neither significant loss of PMFs, increase in growing follicles, nor decrease in nuclear FOXO3A were observed in non-AA–treated ovaries. No increased expression of cleaved caspase-3 was seen in PMFs within the ultrashort time interval after AA or non-AA chemotherapy. Significant stromal fibrosis and neovascularization were observed in AA-treated ovaries only after follicle loss had already occurred (4–6 months). Conclusion(s): Follicle activation occurs in vivo in ovaries of patients treated with AA, indicating a pathologic mechanism which may contribute to chemotherapy-induced follicle loss.