<prompt> Which among the following is not naturally occurring estrogen?EstroneEstradiolEstriolDiethylstilbestrol  <response>: Estrone, Estradiol and Estriol are natural estrogens The biologically active estrogen is estradiol Estrone and estriol are weaker estrogens Adipose tissue and liver conve androstenedione into estrone Diethylstilbesterol is a synthetic, non-steroidal estrogen of the stilbestrol group. DES is known to cause clear cell carcinoma, a rare vaginal tumor in girls and women who had been exposed to this drug in utero. Ref: Shaws Textbook of Gynaecology, 15th edition, page no: 309 