Survival after breast cancer in women with a subsequent live birth: Influence of age at diagnosis and interval to subsequent pregnancy.

Background: There remains a considerable concern among both patients and oncologists that having a live birth (LB) after breast cancer might adversely impact survival.

Methods: analysis of survival in a national cohort of women with breast cancer diagnosed at age 20-39 years between 1981 and 2017 (n = 5181), and subsequent LB using Scottish Cancer Registry and national maternity records. Cases had at least one subsequent LB, each was matched with up to six unexposed cases without subsequent LB, accounting for guaranteed time bias.

Results: In 290 women with a LB after diagnosis, overall survival was increased compared to those who did not have a subsequent LB, HR 0.65 (95%CI 0.50-0.85). Women with subsequent LB who had not had a pregnancy before breast cancer showed increased survival (HR 0.56, 0.38-0.82). There was a progressively greater interaction of subsequent LB with survival with younger age, thus for women aged 20-25 years, HR 0.30 (0.12-0.74) vs. those aged 36-39, HR 0.89 (0.42-1.87). In women with LB within five years of diagnosis, survival was also increased (HR 0.66; 0.49-0.89). Survival following LB was similar to unexposed women by ER status (both positive and negative) and in those known to have been exposed to chemotherapy.

Conclusions: This analysis provides further evidence that for the growing number of women who wish to have children after breast cancer, LB does not have a negative impact on overall survival. This finding was confirmed within subgroups, including the youngest women and those not previously pregnant.