Peppercorn, Jeffrey

10065 Background: Prospective data regarding fertility and pregnancy after breast cancer are limited. Many young survivors are interested future fertility, but pregnancy rates among women attempting and not attempting pregnancy have not been studied prospectively. Methods: As part of a multicenter cohort study, women diagnosed age ≤40 with stage 0-3 breast cancer are surveyed at baseline then annually regarding fertility interest, attempts, and pregnancies. Chi-square tests were used to compare proportions attempting and achieving pregnancy. Results: At least once in the 5 years (yrs) after Dx, 334/959 (35%) women reported interest in future biologic children. The percent interested was stable in the first 3 yrs then declined: 256 (27%, baseline), 244 (27%, 1 year), 209 (25%, 2 yrs), 176 (25%, 3 yrs), 106 (18%, 4 yrs), and 72 (16%, 5 yrs). Pregnancy was attempted by 104/334 (31%) of women who reported interest and 4/625 (1%) who did not. Pregnancy occurred in 118 women (12%), including 76/108 (70%) who attempted and 42/851 (5%) who did not. Attempts and achieving pregnancy were associated with younger age, partnered status, and not having children prior to Dx (table). Lower stage was associated with attempting pregnancy and ER negative disease with achieving pregnancy. Conclusions: A substantial number of young women become pregnant in the 5 years after a breast cancer diagnosis. Given that over 1/3 of pregnancies were among women who did not report attempting, additional attention to contraception counseling should be considered. Further evaluation of assisted reproductive technology use, pregnancy and disease outcomes in this cohort, and the POSITIVE Trial (NCT02308085) will shed light on the feasibility and safety of pregnancy after breast cancer. [Table: see text]