Which of the following is not a tumour marker?
AAFP
BABG
CCA 125
DPSA
Answer:
B. ABG
Read Explanation:
Tumour Markers Overview
- Definition: Tumour markers are substances, often proteins, that are produced by cancer cells or by other cells in the body in response to cancer or certain benign conditions. They are found in blood, urine, stool, tumour tissue, or other bodily fluids.
- Clinical Utility: They are used to help detect, diagnose, stage, and monitor the progression of cancer. They can also indicate how well a patient is responding to a treatment.
- Limitations: Most tumour markers are not diagnostic on their own because their levels can also be elevated in non-cancerous conditions. Therefore, they are typically used in conjunction with imaging, biopsies, and clinical evaluation.
Common Examples of Tumour Markers
- PSA (Prostate-Specific Antigen): Used to screen for and monitor prostate cancer.
- CA-125: Primarily associated with ovarian cancer.
- CEA (Carcinoembryonic Antigen): Often used for colorectal cancer monitoring and follow-up.
- AFP (Alpha-fetoprotein): A marker for liver cancer (hepatocellular carcinoma) and germ cell tumours.
- CA 19-9: Frequently used for pancreatic and biliary tract cancers.
- Beta-hCG: Elevated in certain germ cell tumours and gestational trophoblastic disease.
- HER2/neu: Often tested in breast and gastric cancer to determine suitability for targeted therapies like Trastuzumab.
Key Diagnostic Distinctions
- Specificity: A high-specificity marker is rare; most markers have low specificity, meaning false positives are common.
- Sensitivity: Many early-stage cancers do not produce high enough levels of markers to be detected in blood tests, leading to false negatives.
- Standard Practice: Due to these limitations, medical guidelines do not generally recommend tumour marker testing as a primary screening tool for the average-risk general population, with the notable exception of PSA testing in specific age groups.