17β-HSD2 (17β hydroxysteroid dehydrogenase type 2) belongs to the 17β-HSD family of proteins that regulate the availability of steroids within a tissue. 17β-HSD2 converts active steroids to their inactive form through its oxidative activity. It is a key player in the inactivation of Estradiol and testosterone. Due to the affects that 17β-HSD2 has on the availability of estrogen, it has been extensively investigated for playing a possible role in breast tumor development, colon cancer development and the pathophysiology of endometriosis.