Which hormone is primarily responsible for the growth of leiomyomas (fibroids)?

Estrogen is primarily responsible for the growth of leiomyomas, commonly known as uterine fibroids. These benign tumors are sensitive to fluctuations in hormone levels, especially estrogen. During the reproductive years when estrogen levels are highest, these tumors can grow more rapidly. The presence of estrogen stimulates the proliferation of smooth muscle cells and increases blood flow to the uterus, which supports fibroid growth.

While progesterone also has effects on the uterus, particularly in the menstrual cycle and pregnancy, it does not promote the growth of leiomyomas to the same extent that estrogen does. Testosterone is not significantly involved in the growth of leiomyomas, and human chorionic gonadotropin primarily plays a role in pregnancy and does not have a direct effect on fibroid growth. Therefore, estrogen's central role in stimulating the development and growth of leiomyomas makes it the correct choice in this context.