During a women's pregnancy, cells in the developing placenta (the sac that nourishes the egg after it’s fertilization) makes Human Chorionic Gonadotropin or hCG. Some cancerous tumors also produce these hormones. The test can measure elevated levels of the hormones and can help in diagnosing cancer in patients. It is also used to help diagnose gestational trophoblastic disease (GTD). Combined with other tests such as AFP and lactate dehydrogenase, to help diagnose germ cell tumors.
GTD is a group of tumor that develops inside a woman's uterus. As hCG is not commonly present in men or nonpregnant women, it is useful to detect cancerous tumors.