Fertility among young breast cancer survivors attempting pregnancy: A prospective, multicentre cohort study.

1518 Background: Despite high interest among young women diagnosed with breast cancer (BC) in future fertility, prior research has been hampered by short follow-up and lack of prospective assessment of pregnancy attempts. We sought to describe fertility outcomes among young women participating in a prospective cohort who reported pregnancy attempt post-BC diagnosis. Methods: Women with stage 0-III BC in the Young Women's Breast Cancer Study (YWS, NCT01468246), a multicenter, prospective cohort of women diagnosed at age ≤40 from 2006-2016 who reported attempting pregnancy post-diagnosis were included. Those with prior hysterectomy, bilateral oophorectomy, or metastatic disease at diagnosis were excluded. Data on attempting pregnancy and fertility outcomes were obtained from serial surveys. Multivariable logistic regression with stepwise model selection was used to identify factors associated with pregnancy and live birth. Results: Among 1213 eligible participants, 197 reported any attempt of pregnancy (16%) over a median follow-up of 11 years (range: 3-17). Among attempters, median age at diagnosis was 32 years (range: 17-40); 74% were non-Hispanic White; 41% had stage I, 35% stage II, 10% stage III, and 14% stage 0 BC; 76% had HR+ disease; 68% received chemotherapy; 57% received endocrine therapy within one year post-diagnosis; 13% were BRCA1/2 pathogenic variant (PV) carriers; 51% reported financial comfort at baseline; 51% were nulligravida and 72% nulliparous at diagnosis; 28% had undergone fertility preservation consisting of egg/embryo freezing at diagnosis; 15% reported a history of infertility before BC diagnosis. Most (73%) reported ≥1 pregnancy after diagnosis and 65% reported ≥1 live birth. Median time from diagnosis to first pregnancy was 48 months (range: 6-125). In the multivariable model, greater age at diagnosis (odds ratio OR 0.82 per year increase, 95% CI 0.74-0.90, P<0.0001) was negatively associated with pregnancy, while financial comfort at baseline (OR 2.04, 95% CI 1.01-4.12, P=0.047) was predictive of pregnancy. For live births, greater age at diagnosis was negatively associated (OR 0.82 per year increase, CI 95% 0.76-0.90, P<0.0001) while having undergone fertility preservation at diagnosis was predictive (OR 2.78, 95% CI 1.29-6.00, P=0.009). History of infertility, nulliparity at diagnosis, tumor characteristics, cancer treatment, race, ethnicity, and BRCA1/2 PV status were not associated with either outcome. Conclusions: This is the first prospective study with greater than 10 years of follow-up to report fertility outcomes in young BC survivors accounting for attempting pregnancy. The majority achieved a pregnancy and most reported a live birth. Our findings can be incorporated into the counseling of young BC patients and survivors, and highlight the need for accessibility of fertility preservation services for this population. Clinical trial information: NCT01468246 .