Although a number of studies have looked at what happens to breast tissue when women start using hormone replacement therapy, the impact of continuing and discontinuing hormone use has not been well understood.

CNN: Health - Hormone replacement may influence mammography accuracy

However, radiologists who do the actual mammography screenings have long known hormone use can change breast tissue.

CNN: Health - Hormone replacement may influence mammography accuracy

These hormones include cortisol (which is related to stress), estradiol (the main female sex hormone) and prolactin (which, as its name suggests, triggers her breast tissue to develop the ability to secrete milk).

ECONOMIST: Hormones and fatherhood