Goserelin often used in cancer treatment. It is a GnRH angonist, stopping production of LH by the pituitary gland. Agonists do this by flooding the pituitary gland with LH, desensitizing it.
LH tells the reproductive organs to produce either estrogen (along with or testosterone, therefore blocked or slowed production of LH leads to decreased hormone levels.
Goserelin (Zoladex) can be used as a puberty blocker and also in the treatment of endometriosis, fibroids, and in assisted reproduction.