Abstract P4-11-05: Safety of fertility preservation indicated by a diagnosis of breast cancer: A Swedish registry-matched cohort study

Purpose The number of women that perform fertility preservation (FP) before initiating chemotherapy for treatment of breast cancer is increasing. Our purpose was to investigate the safety of performance of fertility preservation with and without hormonal stimulation in the incidence rate of breast cancer relapse. Patients and methods The study was designed as a matched cohort study. Women who had undergone FP at the Reproductive Medicine clinic of Karolinska University Hospital (N=187), irrespective of whether hormonal stimulation was required or not, were considered exposed. For all exposed women, two age-matched women who had not undergone fertility preservation were identified in the Regional Breast Cancer Registry Stockholm-Gotland and the Swedish National Quality Registry for Breast Cancer (N=319). The proportional hazards assumption was evaluated by applying the Grambsch-Therneau test on the Schoenfeld residuals obtained from each model, respectively. When interpreting the test results, a significance level of 5% was used to determine statistical significance. Results In the exposed cohort, a higher proportion of women underwent FP with hormonal stimulation aiming at freezing eggs or embryos (81%, N=142), whereas only 19% underwent freezing of ovarian tissue or attempted egg retrieval without hormonal stimulation (N=35). The mean follow up time was 6.3 years (range: 1.5-17.8 years), and median follow-up: 5.7 years. There was no evidence of non-proportional hazards with respect to the effects of fertility preservation on the risk of relapse in the whole FP cohort, irrespective if the women underwent hormonal stimulation or not for FP, or of receptor status or tumour size at diagnosis. A stratified Cox regression model that allowed separate baseline hazard functions for each level for the investigation of the effect of number of involved lymph nodes was performed. In this model, the effect of fertility preservation on the risk of relapse was virtually unchanged (IRR: 1.02, 95% CI:0.56-1.84). Conclusion Fertility preservation either using hormone stimulation or not is unlikely to cause substantially increase recurrence risk of breast cancer, and irrespective of the receptor status, tumorur size of lymph node compromise. The incidence of breast cancer relapse after hormonal or non-hormonal fertility preservation was not different from that of matched controls from the Regional Breast Cancer Registry in this large cohort study. Citation Format: Rodriguez-Wallberg KA, Eloranta S, Krawiec K, Lissmats A, Liljegren A. Safety of fertility preservation indicated by a diagnosis of breast cancer: A Swedish registry-matched cohort study. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-11-05.