Tumor Markers Lecture PDF

Cancer and tumor markers Cancer is the uncontrolled growth and spread of abnormal cells in the body. Cancer is not a single disease; it is a group of more than 200 different diseases identified by uncontrolled cell growth and proliferation. Malignant tumors: Malignant tumors are cancers....

Cancer and tumor markers Cancer is the uncontrolled growth and spread of abnormal cells in the body. Cancer is not a single disease; it is a group of more than 200 different diseases identified by uncontrolled cell growth and proliferation. Malignant tumors: Malignant tumors are cancers. Cancer cells can invade and damage tissues and organs near the tumor. The invasive properties distinguish cancer cells from normal cells. Modifications (mutations) in the benign cells enable them to invade the surrounding tissues and spread (metastasis) to other parts of the body. Examples: 1. Membrane modifications in cancer cells decrease cell- cell interactions and adhesion. 2. Production of proteases facilitate movement of cells through the extracellular space. Benign tumors: Benign tumors are not cancer. They can be removed, and in most cases they do not come back. Most important, cells from benign tumors remain in one location and do not spread to other parts of the body. Examples of benign tumors Adenoma A tumor that grows in and around the glands Lipoma A tumor in fatty tissue Myoma A tumor of muscle tissue Angioma A tumor usually composed of small blood or lymph vessels (e.g. a birth mark) Chondroma A tumor of cartilage. Stages of cancer: Stage 1: Confined to organ of origin. Stage 2: Locally invasive. Stage 3: Spread to lymph nodes. Stage 4: Spread to distant sites.  Tumor markers A tumor marker is a substance (protein, enzyme, etc) produced by a tumor, or by the host in response to a tumor, Can be used to differentiate a tumor from normal tissue, or to determine the presence of a tumor. Such substances are found in cells, tissue, or body fluids, and can be measured qualitatively or quantitatively by chemical, immunological, or molecular diagnostic methods. As tumor cells multiply, cancer spreads, and tissue is damaged, these substances increase and leak into the bloodstream. Measurement or identification of tumor makers is useful in tumor diagnosis, to follow the treatment efficiency, and to predict the response to the therapy. Diagnostic methods for neoplasia: 1. Family history and direct examination: Symptoms such as weight loss, fatigue, and pain may be present. A mass may be palpable or visible. 2. Radiographic techniques: imaging techniques used to detect the presence and location of mass lesions. X-rays. Computed tomography (CT). Magnetic resonance imaging (MRI). Mammography. Ultrasonography (ultrasound). PET scan. 3. Pathological diagnostic procedure: FNA (fine needle aspiration), biopsy, cytological smears. 4. Biochemical assays and genetic methods: tumor markers. Methods used to measure tumor markers: 1. Immunoassays (e.g. ELISA). 2. HPLC. 3. Immunohistochemistry. 4. Enzyme assays. 5. Molecular biology methods. Types of tumor markers: 1. Cell surface antigens 2. Cytoplasmic proteins 3. Enzymes 4. Hormones 5. Oncofetal antigens 6. Receptors 7. RNA or DNA biomarkers. 8. Gene expression markers. The ideal tumor marker would be: 1. Specific for a tumor: few markers are specific for a single individual tumor 2. Sensitive: to detect small tumors to allow early diagnosis or use in screening. 3. Level should correlate/ change in response to tumor size. 4. Levels in healthy individuals are at much lower concentration than in cancer. 5. Easily and reproducibly measured. 6. Determination is not expensive. No known tumor marker now has sensitivity and 100% specificity. In practice, tumor markers are most useful in evaluating the progression of disease status after the initial therapy and monitoring subsequent treatment modalities. Urinary tumor markers: CSF tumor markers: False results in tumor markers: False positive results occur with: 1. Inflammatory conditions 2. Benign conditions 3. Presence of liver diseases that affect metabolism and excretion of some tumor markers as AFP, CEA, CA 19-9, CA 15-3 4. Disturbances of renal function that affect levels of some tumor markers as calcitonin, PSA, CEA, CA 5. As a consequence of different physiological conditions, e.g. in pregnancy: ß-HCG, AFP False negative results occur with: 1. Insufficient expression of a certain antigen or production in only some of tumor cells 2. Insufficient blood circulation in the tumor 3. Rapid degradation clearance of antigens Limitations of the use of tumor markers: Tumor markers are not ideal compounds for diagnosis of cancer for two reasons: 1. False positive results: individuals without cancer may have elevated levels of the tumor marker. 2. False negative results: tumor markers are not sufficiently elevated in all individuals with cancer. Examples of false results: 1. One of the most commonly used tumor markers is prostate- specific antigen (PSA). It is present in all adult males, but its level is increased after both benign and malignant changes in the prostate. Therefore, high levels of PSA indicate only that further tests are required to determine whether the condition is cancer. If prostate cancer is diagnosed, the levels of PSA can help to determine the effectiveness of treatment. 2. The tumor marker is CA125, which is produced by a number of different cells, particularly ovarian cancer cells. CA 125 is also increased in menstruation, first-trimester pregnancy, benign ovarian cysts, cirrhosis, renal failure, etc. So, it is not used as a routine test for ovarian cancer. Many common conditions that cause inflammation also increase the level of CA125, leading to a high incidence of false positives It is used primarily to monitor the treatment of ovarian cancer. When the cancer is responding to treatment, CA125 levels fall. CA-125: cancer antigen 125, carcinoma antigen 125, or carbohydrate antigen 125. 3. ESR and the activity of LDH are classical tumor markers. These markers are also increased in inflammation and necrosis process, and that is why they are highly nonspecific for malignancy. So, tumor markers with few exceptions are not adequate for primary diagnosis of malignancy…… Combination of tumor markers may increase diagnostic sensitivity. Common serum markers for cancer diagnosis/prognosis: AFP CEA CA CA CA PSA PAP HCGb NSE 15-3 19-9 125 Lung x x x x x x Pancreas x x x x x Kidney x x x Breast x x x Ovarian x x x x X Cervical x x Uterine x x x x Prostate x x Liver x x x x x Gastro x x x Colon x x x x Bladder x Leukemia x Testicular x x x Tumor markers can be used for: 1. Determining the effectiveness of cancer treatment. 2. Detecting tumor recurrence or remission. Some common tumor markers: Analyte Cancer Use CEA Monitor colorectal, breast, lung cancer. CA-125 Ovarian cancer monitoring. CA15-3 monitor recurrence of breast cancer. AFP Germ cell tumors, liver cancer. Total PSA Screen and monitor prostate cancer. Free PSA Distinguish prostate cancer from benign prostate hyperplasia. HCG Germ cell tumors. Hormone receptors Breast cancer therapy. Classification of tumor markers: 1. Oncofetal proteins (normally produced by the fetus): α-fetoprotein (AFP): increased in primary liver cancer. Human chorionic gonadotropin (hCG). Carcinoembryonic antigen (CEA): colorectal and other cancers such as pancreatic, gastric, lung, ovarian, etc. 2. Carbohydrate antigen: CA-125: ovarian cancer, good for monitoring of response and recurrence. CA-19-9. 3. Enzymes (examples): Lactate dehydrogenase, alkaline phosphatase, amylase, creatine kinase. Prostate specific antigen (PSA) and prostatic acid phosphatase (PAP): increased in prostatic carcinoma. Neuron-specific enolase (NSE): in tumors of neuroendocrine origin such as neuroblastoma. 4. Hormones and hormone receptors: Breast estrogen and progesterone receptors. ACTH and other endocrine hormones. 5. Proteins as tumor markers: Β2- microglobulin, ferritin. 6. Genetic makers: e.g. oncogenes and tumor suppressor genes. Mutated N-ras gene (oncogene): in neuroblastoma. Mutated K-ras gene: in pancreatic, colon, lung and bladder cancers. BRCA1 and BRCA2: in breast cancer. Oncofetal proteins: e.g. Alpha-fetoprotein (AFP): AFP is a normal fetal serum protein (its level is 3 mg/ml). It is normally synthesized by the fetal liver. In adult serum, AFP level is less than 20 ng/ml. Clinical applications of AFP: 1. Diagnosis, staging, prognosis, and treatment monitoring of hepatocellular carcinoma. 2. AFP is also elevated in testicular germ cell tumors. The AFP is also elevated in acute viral, or drug induced hepatitis, however, these elevations are under 500 ng/ml. AFP is a useful marker in hepatocellular carcinoma and germ cell tumors, the only conditions associated with extreme elevations greater than 500 ng/ml. Enzymes as tumor markers: 1. Alkaline phosphatase (ALP) occurs in liver, bone or placenta; however, the ALP in the serum of normal adult originates primarily in liver or biliary tract. The serum ALP activity can be used for assessment of liver metastasis. 2. Elevated levels of lactate dehydrogenase (LDH) in cancer are nonspecific, found in various cancer including liver, acute leukemia, neuroblastoma, and other carcinomas of colon, breast, stomach, and lung. 3. Prostate-specific antigen (PSA): PSA is the only marker used to screen for prostate cancer (although some medical groups do not recommend its use). PSA has at least one of the characteristics of an ideal tumor marker- tissue specificity; it is found in normal prostate epithelium and secretions but not in other tissues. It is a glycoprotein, whose function is to liquefy semen. PSA is highly sensitive for the presence of prostate cancer. The elevation is correlated with stage and tumor size. It is predictive of recurrence and response to treatment. Unfortunately, PSA is detectable in normal men and often is elevated in benign prostate hypertrophy, which may limit its value as a screening tool for prostate cancer. PSA determination combined with physical exam is a good method of detecting prostate cancer. Hormones (examples): 1. Insulin production by islet cell tumor. 2. Calcitonin by medullary thyroid carcinoma. 3. Catecholamines production by pheochromocytoma. 4. “Ectopic” ACTH and ADH by lung cancers. Note that these hormones are not normally produced by lungs. 5. Human chorionic gonadotropin (HCG) HCG is normally produced by cells of the placenta during pregnancy. HCG is sensitive, being elevated in women with minute amounts of tumor. The level of HCG is occasionally elevated in breast, lung, and gastrointestinal tract cancers.  Neurophysins are carrier proteins for transport of oxytocin and vasopressin to the posterior pituitary from the hypothalamus. In conclusion: More accurate tumor markers: Recently, patterns of gene expression and changes to DNA have also begun to be used as tissue-specific tumor markers. Cancer researchers are turning to proteomics (the study of protein structure, function, and patterns of expression) in hopes of developing specific and sensitive biomarkers that can be used to: Identify disease in its early stages. Predict the effectiveness of treatment. Predict the chance of cancer recurrence after treatment has ended. Advances in tumor biomarkers: Genomics and proteomics approaches in tumor markers: 1. Complementary DNA (cDNA). 2. microRNA (miRNA) biomarkers. 3. Long non-coding RNA (LncRNA) biomarkers. 4. Protein, and tissue microarray. 5. Mass spectrometry (MS). 6. Bioinformatics tools. 7. Serum proteomics.