Tumor Marker:- Part 8 – Alpha-Fetoprotein (AFP)
- The patient serum is needed.
- Can take a random sample, and no fasting needed.
- For the diagnosis of liver cell carcinoma.
- Patients with chronic active hepatitis.
- Patients with cirrhosis and positive serology (HBV and HCV) should be tested with AFP and ultrasound abdomen.
- AFP is a tumor marker for yolk sac tumors.
- AFP raised in hepatoid gastric carcinoma.
- This is a glycoprotein. This consists of a single polypeptide chain and has a 4% carbohydrate.
- The yolk sac produces this in small amounts and the liver with the abundant amount in the fetus.
- It is normal after about 18 months of birth.
- It is close to albumin, genetically and structurally.
- Gene coding for both is chromosome 4q.
- Its concentration is 10% that of the albumin.
The function of the AFP:
- AFP has increased in pregnancy, usually not >100 ng/mL.
- Its main role is to bind and transport substances that are not water-soluble, like steroids hormones, lipids, vitamins, and bilirubin.
- Maternal serum AFP is lower than expected in Down’s syndrome.
- Maternal serum AFP is raised or higher level in the neural tube defect.
- Level > 1000 µg/L indicate malignancy.
- At this level, 50% of liver cell carcinomas are diagnosed.
- It is ideal for diagnosing a liver tumor below the size of 5 cms.
- To find these small tumors cut-off value has to be set at a lower level between 200 to 1000 µg/L.
- In healthy individuals is 10 µg/L.
This is a tumor marker for:
- Liver cell carcinoma.
- AFP is raised in 80% of liver cell carcinoma.
- >500 ng/mL is diagnostic of liver cell carcinoma.
- AFP may be raised for 18 months before the S/S appears.
- AFP is a sensitive indicator of recurrence.
- AFP >1000 ng/mL in 50% of the cases indicates tumor size >3 cms in diameter.
- In 90% of the cases AFP >200 ng/mL, and 70% have concentration of AFP >400 ng/mL.
- In benign diseases, AFP >400 ng/mL is extremely rare.
- This is more likely raised in immature carcinoma than the mature type of carcinoma.
- Initial high level indicates a poor prognosis.
- Failure to come to normal indicates a problem with surgery where there is incomplete resection or metastasis.
- The postoperative decrease followed by an increase in the AFP indicates recurrence.
- If there is a short doubling in the AFP value, suggest metastasis at the time of surgery.
- AFP is a tumor marker of the Germ cell tumor (nonseminomatous tumor).
- Yolk sac tumors lead to an increase in AFP, which correlates with the tumor prognosis, e.g.,>1000 ng/mL associated with poor prognosis.
- Embryonal cell carcinoma in 27% of the cases.
- Malignant teratoma in 60% of the cases.
- Testicular teratocarcinoma is seen in 75% of the cases.
- Choriocarcinoma element is seen in seminoma, yolk sac, teratoma, and embryonal cell carcinoma.
- Pancreatic carcinoma AFP is positive in 23% of the cases.
- Gastric carcinoma AFP 18% positive.
- Bronchogenic carcinoma 7% positive.
- Colon carcinoma 5% positive.
- AFP is useful for liver cell carcinoma:
- Monitor therapy.
- Adult = <40 ng/mL (<40 µg/L)
- Child <1 year = <30 ng/mL
- Note: In some books on the same page, the values are given in ng/mL and ng/dL. For me difficult to decide which one I can follow.