Curious phenomenon of 'hook effect' in invasive mole

Area of Science:

• Gynecology
• Oncology
• Endocrinology

Background:

• Gestational trophoblastic disease encompasses pregnancy-related trophoblastic tumors.
• Gestational trophoblastic neoplasia includes invasive mole, choriocarcinoma, placental site trophoblastic tumor, and epithelioid trophoblastic tumor.
• Elevated beta human chorionic gonadotropin (β hCG) levels are characteristic, often exceeding 100,000 mIU/mL.

Observation:

• A rare case of invasive molar pregnancy in a woman in her mid-30s presented with bleeding, abdominal mass, hypertension, and hyperthyroidism.
• Initial urine β hCG test was negative.
• Serum β hCG, after dilution, was recalculated to over 850,000 mIU/mL, indicating the 'hook effect'.
• MRI confirmed invasive mole.

Findings:

• The 'hook effect' can cause falsely low or negative hCG results in immunometric assays when levels exceed 500,000 mIU/mL.
• Dilution of serum samples is crucial for accurate β hCG quantification in suspected high-level cases.
• Successful treatment with methotrexate chemotherapy post-hysterectomy led to normalized β hCG levels and 14 months of disease-free survival.

Implications:

• Accurate β hCG measurement is critical for diagnosing and monitoring gestational trophoblastic neoplasia.
• The 'hook effect' must be considered in patients with suspected high β hCG levels, necessitating sample dilution.
• This case highlights the importance of thorough diagnostic workup, including serial dilution of serum samples, for rare presentations of gestational trophoblastic neoplasia.