Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (283 page)

   High-risk patients are indicated by initial serum titer >40,000 mIU/L. Frequent follow-up titers are indicated after radiation therapy with lifelong titers every 6 months.

   Measurement of hCG in the CSF (ratio of serum to CSF <60:1) is used in the diagnosis of brain metastases.

   Limitations of hCG Testing

   Beware of false low results due to artifactual “hook effect” of immunoassays due to large antigen excess (>1 × 10
⁶
mIU/L); this is eliminated by a two-stage immunoassay.

   Clinical and biochemical evidence of hyperthyroxemia may occur because α subunits of TSH and hCG are identical.

   Clinical Presentation

Persistent gestational trophoblastic disease or invasive mole
occurs when the villi are present within the myometrium or its vascular spaces (invasion) and may occur with either PHM or CHM. Following invasion, trophoblasts may embolize to distant sites (metastatic). This type of mole requires surgical resection and usually responds to chemotherapy.

   Laboratory Findings

   HCG may plateau or rise following evacuation of the uterus.

   Endometrial curettings reveal minimal residual villous tissue.

   Clinical Presentation

Placental site trophoblastic tumor
, previously known as trophoblastic pseudotumor, presents as a mass in the endometrium that can be identified on sonogram. These tumors are not well understood and are primarily seen in reproductive age women with rare cases in postmenopausal women. It may follow a normal term delivery, abortion, or a molar pregnancy. Women present with irregular bleeding months to years following the preceding pregnancy. The tumor is composed of cytotrophoblasts, which invade in a pattern similar to normal placental implantation. Immunohistochemistry may help differentiate this tumor from choriocarcinoma. Prognosis for poor outcome is suggested by the length of time from the previous pregnancy. Diagnosis >2 years following the pregnancy has a worse outcome.
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   Laboratory Findings

   HCG measurement reveals persistent low levels (<50 mIU/L).