O-196 Age at diagnosis, previous pregnancy and interval to pregnancy influence survival after breast cancer in women with a subsequent live birth
Authors: Anderson R , Lambertini M , Hall P , Wallace H , Morrison D , Kelsey T 
Published: June 2022

Abstract

Study question
Does subsequent live birth (LB) after breast cancer affect survival, and what are the factors that influence this?

Summary answer
Overall survival was increased in women who had a LB after breast cancer, including in those aged &lt;30 at diagnosis and without a previous LB.

What is known already
As a hormone-sensitive cancer, there has long been concern among both patients and oncologists that having a subsequent pregnancy and LB might impact recurrence and survival. Some analyses have shown no adverse effect, but there remains limited data on this, especially regarding the patient characteristics that might have an influence. This is of growing importance given that age at birth is increasing, so more women with breast cancer will not have started or completed their family.

Study design, size, duration
We performed a retrospective cohort study using national cancer and maternity databases. Women with breast cancer aged less than 40 years diagnosed between 1981 and 2017 were identified from Scottish Cancer Registry records (n = 5181). Pregnancies were included up to end of 2018.

Participants/materials, setting, methods
Women with LB entered study at date of LB, with the primary outcome being subsequent survival. To account for guaranteed time bias, up to 6 matched controls for each exposed case were chosen at random (min = 4, mean = 5.8), matched by similar year of diagnosis and were alive when their match had a LB (i.e date of study entry). Subgroup analyses were by tumour stage, previous pregnancy, and age at diagnosis.

Main results and the role of chance
After excluding 70 women where breast cancer was diagnosed during pregnancy, there were 290 women with a subsequent LB after diagnosis. Overall survival was increased in women with a subsequent LB, HR 0.65 (95%CI 0.50-0.85, p = 0.0015). Women with a subsequent LB who had not had a pregnancy before breast cancer diagnosis showed increased survival (HR 0.56, 0.38-0.82, p = 0.003); this was not found in women who had had a previous pregnancy (HR 0.76, 0.53-1.09). Women with stage 1 disease did not show an effect of subsequent LB (HR 0.74, 0.40-1.35) with similar results in women with stage 2/3 disease (HR 0.71, 0.37-1.37).
Analysis of the effect of age at diagnosis showed a progressively greater interaction of subsequent LB on survival with younger age. For those aged 20-25 years, HR was 0.30 (0.12-0.74; p = 0.009), aged 26-30, HR 0.58 (0.38-0.88, p = 0.011), aged 31-36, HR 0.67 (0.44-1.01, p = 0.057) and aged 36-39, HR 0.89 (0.42-1.87, p = 0.76). In women who had a LB within 5 years of diagnosis, survival was increased, HR 0.66 (0.49-0.89; p = 0.006). Fewer women had a LB 5 or more years after diagnosis (n = 108 vs 182 within 5 years), with no clear effect on survival (HR 0.63, 0.36-1.13).

Limitations, reasons for caution
In the absence of randomised recruitment and selection, minimisation of bias is essential for the validity of the data. The use of national databases avoids selection bias and increases the size of the population studied, and we accounted for guaranteed time bias.

Wider implications of the findings
This analysis provides robust evidence for the growing number of women who wish to have children after breast cancer, that LB does not have a negative impact on overall survival. This was confirmed across age at diagnosis, and by previous pregnancy and timing of subsequent pregnancy.

Trial registration number
Not applicable