Does hormone replacement therapy for menopausal symptoms cause breast cancer?

It can.: The cause of breast cancer is so complex and poorly understood that it's better to talk about "associations" rather than "causes". Studies have shown that women who have used hormone replacement have a slightly higher incidence of breast cancer as compared to women that have not. In general, if you can avoid it, it's better to, especially if you have other risk factors for breast cancer.

In short, no.: There are three human esrogens: Estradiol (from the ovary), estriol (from the placenta in pregnancy) and estrone (from peripheral fat conversion). Estrone is probably the culprit since women with excess peripheral body fat have increase rates of estrogen related cancers (breast, uterus, ovary, colon). Many oral estrogen hormones on the market are converted to estrone in the liver.

Increases risk: Hormone replacement therapy (hrt) has been shown to increase one's risk for breast cancer if taken for longer than 5 years. The current recommendation is to take low doses for a limited amount of time and then stop. There are some other non hormonal medications that can be used to help manage menopausal symptoms.

Depends: Virtually all of the studies showing that hrt increases breast cancer have been done on premarin (conjugated estrogens). Premarin (conjugated estrogens) is converted to estrone in the liver when taken orally. Overweight women convert adrenal hormones into estrone in peripheral body fat & have increased rates of estrogen dependent cancers (breast, colon, uterine). I suspect the culprit is estrone, not estradiol/estriol, the other human estrogens.