Tamoxifen, a synthetic molecule developed in 1971, was introduced in 1977 to treat breast cancer as it slowed the growth of estrogen-dependent tumors. (High estrogen levels promote the cell proliferation induced by growth factors of the breast cells.)
Tumour under a microscope
Mammogram image of a breast tumour
This type of chemotherapy blocks the natural hormones that can stimulate the growth of cancer cells. Megestrol (Megace) is a synthetic derivative of the naturally occurring steroid hormone, progesterone, and functions in a similar manner.