Generational trends in reproductive factors among women in the US: implications for breast cancer incidence

Over the past century, women in the US are attaining menarche earlier, more likely to have their first birth after age 30 and having fewer births. Parsing the extent to which changes in reproductive factors are contributing to the rising incidence of estrogen receptor positive breast cancer, especially in premenopausal women, is necessary to devise long-lasting and sustainable preventive strategies.