Low doses of alkylating agents do not harm human ovarian tissue destined for cryopreservation

Objective: To investigate the impact of non-gonadotoxic doses of alkylating agents on human ovarian cortex.

Design: Retrospective study.

Setting: Academic research center.

Subject: Biopsies from 78 patients who had undergone ovarian tissue cryopreservation were retrieved and analyzed. Among them, 42 had previously been treated with chemotherapy (alkylating agents, dose <3400mg/m²), making up the chemotherapy group, while 36 had not been given any chemotherapy, constituting the control group.

Mean outcome measures: Follicle count and classification, morphology study, immunostaining for apoptosis (cleaved caspase-3), immunostaining for activation (phospho-Akt), fibrosis (Masson's trichrome) and vascularization (von Willebrand factor and smooth muscle actin).

Results: In the prepubertal group, 271 follicles/mm³ were detected in control patients and 501 follicles/mm³ in chemotherapy-exposed subjects. In the adult group, 4916 follicles/mm³ were found in control patients and 6570 follicles/mm³ in chemotherapy-exposed patients. No difference in follicle density was observed between the two groups in any age category. Neither did we encounter any significant difference in follicle viability according to chemotherapy exposure or age. Proportions of non-growing follicles were >76 % in all age groups, irrespective of chemotherapy exposure, and higher, though not significantly, in the chemotherapy group compared to the control group. There were significantly fewer secondary follicles in the adult chemotherapy group than in the adult control group (p=0.009). Concerning apoptosis, no significant difference was observed between control and chemotherapy subjects in any age groups. Numbers of activated follicles were systematically higher in all age categories in the chemotherapy group than the control group. Areas of atypical follicles were noted in 4 out of 14 prepubertal patients in the chemotherapy group. In these areas, follicle density was 84570 ± 8837 follicles/mm³ and all follicles appeared non-viable but showed no sign of apoptosis.

Conclusion: Low-dose chemotherapy had no major impact on ovarian tissue, suggesting that ovarian tissue exposed to some chemotherapy prior to cryopreservation is comparable to ovarian tissue free of any chemotherapy, as clinically demonstrated by high pregnancy rates after ovarian tissue transplantation in women exposed to chemotherapy. Previous chemotherapy should therefore no longer be a contraindication to ovarian tissue cryopreservation.