Lord SJ et al. - These findings suggest that the effect of parity on a woman's long-term risk of breast cancer is modified by age at first full-term pregnancy and possibly by breastfeeding. Methods
Study to investigate whether age at first birth (<25 or ≥25 yrs) and breastfeeding (ever/never) modify the long-term effect on risk of ERPR(+) and (-) cancer
1,457 incident BCa cases and 1,455 controls ages ≥55 yrs
Results
Women who gave birth before age 25 yrs had a 36% reduced risk of BCa vs nulligravida
This was not observed for women who started their families at an older age
This protective effect was restricted to ERPR(+) BCa
Late age at first birth increased the risk of ERPR(-) cancers
Additional births reduced the risk of ERPR(+) cancers among women with an early first birth
And also among women who breastfed but not among older mothers or those who never breastfed
In women with a late first birth who never breastfed, multiparity was associated with increased risk of BCa
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