Progesterone was first found to be effective in the treatment of endometrial hyperplasia in 1951, and progestins were first found to be effective in the treatment of endometrial cancer in 1959. MGA was reported to be effective in the treatment of endometrial hyperplasia in the mid-1960s. It first started to be studied as a treatment for endometrial cancer in 1967, with findings published in 1973. MGA was reportedly introduced for the treatment of endometrial cancer in the United States in 1971. Progesterone was studied in the treatment of breast cancer in 1951 and 1952, but with relatively modest results. MGA was first studied in the treatment of breast cancer in 1967, and was one of the first progestins to be evaluated for the treatment of this disease. A second study was conducted in 1974. A "breakthrough" and surge of interest in progestins for breast cancer occurred in 1978 when a study using a massive dosage of medroxyprogesterone acetate to treat breast cancer was published. A third study of MGA for breast cancer was published in 1980, and this was followed by additional studies in the 1980s and beyond. MGA was approved for the treatment of breast cancer in the United States by at least 1983.