Clinical meaning
Tumor markers are substances produced by cancer cells or by the body in response to cancer that can be detected in blood, urine, or tissue samples. While tumor markers are valuable tools in oncology, the practical nurse must understand that most tumor markers are NOT used for cancer screening in the general population because they lack sufficient sensitivity (ability to detect all cancers) and specificity (ability to distinguish cancer from non-cancerous conditions). The primary clinical applications of tumor markers are: monitoring treatment response in diagnosed cancers, detecting recurrence after treatment, estimating prognosis, and in some specific cases, aiding in diagnosis when combined with other clinical findings. Prostate-specific antigen (PSA) is a glycoprotein produced by both normal and malignant prostate epithelial cells. While PSA is the most widely used cancer screening marker, it is important to understand that elevated PSA is NOT specific for prostate cancer. Benign prostatic hyperplasia (BPH), prostatitis, urinary tract infection, recent ejaculation, and digital rectal examination can all elevate PSA levels, leading to false-positive results. The normal range is generally considered below 4.0 ng/mL, though age-specific reference ranges are used (higher cutoffs for older men). Carcinoembryonic antigen (CEA) is a glycoprotein normally produced during fetal development. In adults, CEA is associated primarily with colorectal cancer but can be elevated in pancreatic, breast, lung, gastric, and ovarian cancers, as well as in non-malignant conditions such as smoking, inflammatory bowel disease, liver cirrhosis, and chronic lung disease. CEA is most valuable for monitoring treatment response and detecting recurrence in patients with known colorectal cancer. Alpha-fetoprotein (AFP) is a protein produced by the fetal liver and yolk sac. In adults, elevated AFP is associated with hepatocellular carcinoma (liver cancer) and non-seminomatous germ cell tumors (testicular cancer). AFP is also elevated in pregnancy (normal), chronic hepatitis, and cirrhosis. CA-125 (cancer antigen 125) is a glycoprotein associated with ovarian epithelial cancer. However, CA-125 is elevated in many benign conditions including endometriosis, pregnancy, pelvic inflammatory disease, menstruation, liver disease, and other peritoneal irritation, making it unreliable as a general screening tool. It is most useful for monitoring treatment response in diagnosed ovarian cancer. CA 19-9 is a carbohydrate antigen associated primarily with pancreatic cancer and is also elevated in cholangiocarcinoma, gastric cancer, and benign conditions such as pancreatitis and biliary obstruction. Human chorionic gonadotropin (hCG) is normally produced by the placenta during pregnancy but is also a marker for gestational trophoblastic disease (hydatidiform mole, choriocarcinoma) and testicular germ cell tumors (seminoma, non-seminoma). An elevated hCG in a non-pregnant individual requires urgent evaluation. The practical nurse plays a critical role in specimen collection, documentation, patient education about the meaning and limitations of tumor marker results, and emotional support during what is often an anxious waiting period for results.