Recently, I received a call from a physician wanting to measure serum concentrations of human placental lactogen (hPL) to help diagnose a placental site trophoblastic tumor. This was an interesting question that I had never received before.

hPL is a placental hormone (also called human chorionic somatomammotropin) that has a structure similar to human growth hormone (produced by the pituitary gland). It is secreted by syncytiotrophoblasts during pregnancy and helps regulate the metabolic state of the mother during pregnancy. hPL is produced only during pregnancy. It becomes detectable in maternal serum by weeks 5-6 of gestation and its concentration continues to increase during pregnancy with maximum concentrations near term, when it plateaus. Unlike hCG, hPL concentrations rise in parallel to placental weight. In the past hPL has been studied to follow intrauterine growth retardation, and fetal demise, however, hPL reflects only fetal size, not fetal demise, so today it is rarely used to monitor pregnancy.    

Placental site trophoblastic tumor (PSTT) is a rare (2% of gestational trophoblastic neoplasms) form of gestational trophoblastic disease. The most common symptom is vaginal bleeding, however patients may also present with amenorrhea, abdominal pain or uterine enlargement.

Women with PSTT usually have low serum concentrations of hCG with 79% of patients having concentrations < 1,000 IU/L and 58% < 500 IU/L, which can make diagnosis difficult.     

It is generally as slow-growing tumor and hence 10-15% fail to respond to chemotherapy. 25-30% of patients will develop recurrence and ~15% can lead to death. Treatment includes hysterectomy.

These tumors also produce hPL. Studies have shown that 96% of the PSTT specimens stained positive for hPL by immunohistochemistry.

However, measuring hPL concentrations in serum seems to be an urban legend. While a few published studies mention measuring it in serum (here and here), I have been unable to find a single study that has actually measured serum hPL in PSTT patients. In short, while diagnosis of PSTT can be difficult, clinical findings and hCG concentrations remain the most informative. There is no evidence to support the use of serum hPL to diagnose or follow PSTT. Interestingly, when we called the physician to relay this information, he said that he was ordering it because the patient had been seen at an outside clinic and it had been ordered there. This is just another example of how urban legends can spread. As always, I urge health professionals to understand the clinical utility of lab tests before they order.

Originally published by The Pregnancy Lab

About The Author

Professor of Pathology & Immunology, and Obstetrics & Gynecology, Washington University School of Medicine

Dr. Gronowski is a Professor of Pathology & Immunology, and Obstetrics & Gynecology at Washington University School of Medicine (St. Louis Missouri). She is Associate Medical Director of the Clinical Chemistry and Serology & Immunology laboratories at Barnes-Jewish Hospital. Dr. Gronowski received her Ph.D. in Endocrinology- Reproductive Physiology from University of Wisconsin, and is a diplomate of the American Board of Clinical Chemistry. Dr. Gronowski is past president of the American Board of Clinical Chemistry and the American Association for Clinical Chemistry. Her research focuses primarily on the laboratory diagnostics of endocrinology and reproductive physiology with a particular emphasis on maternal fetal medicine. She edited the book entitled “Handbook of Clinical Laboratory Testing During Pregnancy”.