AFP (Alpha-Fetoprotein): Liver Cancer Surveillance, Germ Cell Tumors, and Pregnancy Screening

AFP is the major fetal serum protein, made by the yolk sac and fetal liver during gestation. Levels in the fetus and newborn are extraordinarily high (often above 50,000 ng/mL) and decline rapidly after birth, reaching adult levels (below 10 ng/mL) by about a year of age. In healthy adults it has no major function and is barely detectable.

AFP rises again whenever hepatocytes are regenerating in bulk or have been transformed:

• Hepatocellular carcinoma (HCC), the classic adult oncologic association. Roughly 60 to 70 percent of HCCs produce AFP. Small early-stage HCCs are far less likely to.
• Non-seminomatous germ cell tumors (yolk sac, embryonal, mixed). These cancers recapitulate fetal yolk sac biology, including AFP production.
• Active hepatic regeneration during chronic hepatitis flares, cirrhosis, or recovery from acute hepatitis.
• Pregnancy, from placental and fetal sources.
• Rare hepatic conditions: hereditary tyrosinemia type 1, ataxia-telangiectasia.

For non-pregnant adults outside infancy:

• Below 10 ng/mL: normal in non-pregnant adults.
• 10 to 20 ng/mL: mild elevation. Often seen in chronic hepatitis or cirrhosis without cancer. Warrants context, not panic.
• 20 to 200 ng/mL: moderate elevation. In a cirrhotic patient, raises HCC suspicion. Combined with imaging, often confirms or excludes.
• 200 to 400 ng/mL in cirrhosis: highly suggestive of HCC unless proven otherwise.
• Above 400 ng/mL in cirrhosis with a liver mass: diagnostic of HCC under most international criteria, often without need for biopsy.
• Above 1000 ng/mL: typically advanced HCC or a non-seminomatous germ cell tumor.

Maternal serum AFP in pregnancy is reported as multiples of the median (MoM) for gestational age, not as raw ng/mL. That is a separate clinical workflow and should not be conflated with oncology AFP.

The interpretive question is always the clinical setting. The same AFP value lands in different worlds depending on the patient.

In a cirrhotic patient on HCC surveillance:

• A stable mild elevation (10 to 20) over time often reflects ongoing chronic hepatitis activity rather than cancer.
• A rising AFP, even within the "normal" range, is meaningful. Trends matter more than absolute thresholds.
• An AFP above 200 with a liver lesion on imaging is highly suggestive of HCC.
• An AFP above 400 with a liver mass meeting imaging criteria is generally accepted as diagnostic of HCC without biopsy.

In a young person with a testicular or ovarian mass:

• Elevated AFP suggests a non-seminomatous germ cell tumor (yolk sac, embryonal, mixed types).
• Pure seminomas and pure dysgerminomas typically do not produce AFP. An elevated AFP excludes "pure" classification.
• Combined with beta-hCG and LDH, AFP is part of the IGCCCG risk stratification used to guide treatment.

Common benign causes of elevated AFP:

• Acute or chronic hepatitis (viral, alcoholic, autoimmune).
• Cirrhosis without HCC, especially during regenerative flares.
• Recovery from acute liver injury.
• Pregnancy.
• Hereditary tyrosinemia type 1, ataxia-telangiectasia, hereditary persistence of AFP (rare).

Other malignancies that can raise AFP: hepatoid variants of gastric, pancreatic, and lung adenocarcinoma; rarely, biliary tract tumors. Uncommon, but worth remembering when a markedly elevated AFP shows up without a clear hepatocellular or germ cell explanation.

Low AFP is reassuring in two specific contexts: it is consistent with no detectable HCC in a cirrhotic surveillance population, and in a treated germ cell tumor patient it is consistent with remission. There is no clinically meaningful "too low" AFP in a non-pregnant adult.

A normal AFP does not rule out HCC. Sensitivity of AFP alone for HCC is roughly 40 to 65 percent at standard cutoffs, and small early-stage tumors often produce little or no AFP. This is why AASLD pairs AFP with abdominal ultrasound every 6 months. Neither test alone is sufficient.

Pure seminomas and pure dysgerminomas do not produce AFP. A normal AFP in someone with a testicular or ovarian mass narrows the histology but does not rule out cancer.

AFP trend matters more than any single value, especially in three settings:

• HCC surveillance. A doubling of AFP from a stable cirrhotic baseline, especially a rise that crosses 100 to 200 ng/mL, prompts cross-sectional imaging (multiphase CT or MRI) even when ultrasound is unremarkable.
• After HCC treatment. AFP should fall toward normal after curative resection, transplant, or ablation. A rise from nadir is a recurrence signal, often preceding imaging changes.
• During germ cell tumor treatment. AFP has a known half-life of 5 to 7 days. Failure to fall at the expected rate during chemotherapy is a recognized signal of inadequate response and may prompt treatment intensification per IGCCCG guidance.

In benign chronic liver disease, AFP can wax and wane with disease activity. A persistently rising trend, especially in cirrhosis, is the worrying pattern. Stable mildly elevated values in known chronic hepatitis are usually fine but warrant tighter imaging surveillance.

• AFP above 200 ng/mL in a cirrhotic patient. Multiphase CT or MRI of the liver is indicated.
• AFP above 400 ng/mL plus a liver mass meeting imaging criteria in cirrhosis. Diagnostic of HCC under most international guidelines.
• Rising AFP from a stable cirrhotic baseline, even within the "normal" range. Image, do not wait for the absolute cutoff.
• Elevated AFP in a young person with a testicular or ovarian mass. Proceed urgently to oncologic workup. Non-seminomatous germ cell tumors are often curable but treatment is time-sensitive.
• Failure of AFP to fall at the expected half-life during germ cell tumor chemotherapy. Discuss with oncology.
• Markedly elevated AFP without a clear cause. Workup for hepatoid variants of GI/pulmonary adenocarcinoma after pregnancy and chronic liver disease are excluded.

What does not warrant action: a borderline AFP of 12 to 18 ng/mL in a patient with known chronic hepatitis and stable disease activity, or an isolated mild elevation ordered as part of an undirected "tumor marker panel" in someone with no cirrhosis, no testicular or ovarian mass, and no pregnancy. Repeat once if uncertain. Do not chase.

• Abdominal ultrasound. Paired with AFP every 6 months in HCC surveillance per AASLD. Neither test alone is adequate.
• Multiphase CT or MRI of the liver. Diagnostic imaging when AFP rises or surveillance ultrasound is concerning.
• Beta-hCG and LDH. Paired with AFP in germ cell tumor diagnosis, staging, and monitoring (IGCCCG criteria).
• ALT, AST, alkaline phosphatase, bilirubin, albumin, INR. Characterize the underlying liver disease that determines AFP interpretation.
• Hepatitis B and C serologies. Most cirrhotic surveillance candidates are defined by chronic viral hepatitis status.
• PIVKA-II (DCP). Alternative HCC marker complementary to AFP, used in some surveillance protocols (especially in Asia) to improve sensitivity.