Choriocarcinoma, a very aggressive malignant tumor, arises from gestational chorionic epithelium or, less frequently, from totipotential cells within the gonads (as a germ cell tumor). These tumors are rare in the Western Hemisphere (they occur in about 1 per 30,000 pregnancies in the United States), but are much more common in Asian and African countries, reaching a frequency of 1 in 2000 pregnancies. Approximately 50% of choriocarcinomas arise from complete hydatidiform moles; about 25% arise after an abortion, while the remainder manifest following an apparently normal pregnancy. In most cases, choriocarcinoma presents as a bloody, brownish discharge accompanied by a rising titer of β-hCG in blood and urine, in the absence of marked uterine enlargement, such as would be seen with a mole. In general, the β-hCG titers are much higher than those associated with a mole.
Fig.19.20Completehydatidiformmole.Inthismicroscopicimage,dis-tendedhydropicvilli(below) andproliferationofthechorionicepithelium(above) areevident.(Courtesy of Dr. Kyle Molberg, Department of Pathology, University of Texas Southwestern Medical School,Dallas,Texas.)
MORPHOLOGYChoriocarcinomasusuallyappearashemorrhagic,necroticuterinemasses.Sometimesthenecrosisissoextensivethatlittleviabletumorremains.Indeed,theprimarylesionmay“selfdestruct,”andonlythemetastasestellthestory.Veryearly,thetumorinsinuatesitselfintothemyometriumandintovessels.Incontrastwithhydatidiformmolesandinvasivemoles,chorionicvilliarenotformed;instead,thetumoriscomposedofanaplasticcuboidalcytotrophoblastsandsyncytiotrophoblasts(
Fig.19.21
Bythetimeachoriocarcinomaisdiscovered,widespreadvascularspreadusuallyhasoccurredtothelungs(50%),vagina(30%–40%),brain,liver,orkidneys.Lymphaticinvasionisuncommon.
Despite the extremely aggressive nature of placental choriocarcinoma, these tumors are remarkably sensitive to chemotherapy. Nearly 100% of affected patients are cured, even those with metastases at distant sites such as the lungs. By contrast, response to chemotherapy with choriocarcinomas that arise in the gonads (ovary or testis) is relatively poor. This striking difference in prognosis may be related to the presence of paternal antigens on placental choriocarcinomas that are lacking in gonadal lesions. Conceivably, a maternal immune response against the foreign (paternal) antigens helps clear the tumor by acting as an adjunct to chemotherapy.
Fig.19.21Choriocarcinoma.Thisfieldcontainsbothneoplasticcytotro-phoblastandmultinucleatesyncytiotrophoblast.(Courtesy of Dr. David R. Genest, Brigham and Women’s Hospital, Boston, Massachusetts.) http://ebooksmedicine.net