Human chorionic gonadotropin, or hCG, is a hormone most commonly associated with pregnancy. In females, hCG is typically made in large amounts by the placenta during pregnancy and is detected by a blood or urine test to confirm pregnancy. It is also normal for non-pregnant women and men to make very small amounts of hCG, with blood levels less than 5mIU/mL. If hCG is high in non-pregnant women or men, it may indicate cancer.
Gestational Trophoblastic Disease
Gestational trophoblastic disease is a group of benign and cancerous tumors that develop in the uterus of a woman during pregnancy. Cells that would normally become the placenta instead develop abnormally to form a tumor. Hydatidiform mole, also referred to as molar pregnancy, is the most common form of gestational trophoblastic disease in which these cells develop into an abnormal benign mass. This can occur without any fetal development, called a complete molar pregnancy, or with some fetal development, a partial molar pregnancy. Sometimes a molar pregnancy becomes cancerous, called choriocarcinoma. In patients with trophoblastic tumors, blood levels of hCG are typically abnormally elevated.
Germ Cell Tumors
Germ cells are the immature reproductive cells that eventually become eggs or sperm. Germ cell tumors, which can be benign or malignant, arise from abnormal growth of these germ cells. They typically occur in the gonads -- testes and ovaries -- where germ cells are normally located and can result in high hCG levels. Germ cell tumors can be classified by the appearance of the cells in the tumor, the main types including seminoma and non-seminomas in the testis, and dysgerminoma and non-dysgerminomas in the ovaries. This classification is important as non-seminomas and non-dysgerminomas tend to occur at an earlier age, grow faster, and have a lower survival rate. HCG also tends to be elevated in non-seminoma and non-dysgerminoma tumors, and aids in the identification of tumor type.
Mediastinal Germ Cell Tumors
Germ cell tumors usually occur in the testes or ovaries, but occasionally will arise in other sites. These growths are called extragonadal germ cell tumors. They present as a mass in the chest, brain, or abdomen, and can also result in elevated hCG levels. The upper chest cavity, known as the mediastinum, includes the heart, esophagus, thymus, nerves, blood vessels and lymph nodes. It is the most common extragonadal site for germ cell tumors. It is not known exactly how germ cells get to these extragonadal sites. It is thought that during the early development of a fetus, not every germ cell ends up in the gonads.
Significance of HCG
HCG is an important tumor marker as its presence and amount in the blood can correlate with differences in diagnosis, tumor size, prognosis and treatment. For example, hCG tends to be elevated in non-seminoma tumors of the testis, but low or undetectable in semonimas. The latter tend to be less aggressive, have a better prognosis, and different treatment plan. HCG levels may also be used to monitor the response of tumors to treatment, especially in gestational trophoblastic disease. Following radiation, chemotherapy or surgical removal of an hCG-producing tumor, blood levels should begin to decrease and ideally will return to normal with successful treatment. A persistent elevation of hCG or increasing levels after treatment may indicate the cancer has come back.
- Tietz Textbook of Clinical Chemistry and Molecular Diagnostics; Carl Burtis, et al.
- National Cancer Institute: Testicular Cancer Treatment: General Information about Testicular Cancer, Prognosis and Staging
- Robbins Pathological Basis of Disease; Ramzi Cotran, et al.
- American Cancer Society: Cancer Facts and Figures 2014