<prompt> Answer this question truthfullyWhich serum tumor marker is commonly elevated in patients with Gestational Trophoblastic Disease GTD, Testicular Cancer non-seminomatous, and Mixed Germ Cell tumors?  <response>: <reason> Most notably, the serum tumor marker β-hCG is elevated in patients with Gestational Trophoblastic Disease GTD, Testicular Cancer non-seminomatous, and Mixed Germ Cell tumors. 