Tumor and Cancer
Tumor defined as a disturbance of growth characterized by excessive proliferation of cells without apparent relation to the physiological demands of the organs involved.A tumor does not mean cancer - tumors can be benign (not cancerous), pre-malignant (pre-cancerous), or malignant (cancerous). When a tumor continues to grow and to invade healthy tissue, it is considered to be a cancer.
Oncology is science deals with the etiology, diagnosis, treatment, prevention and research aspects of cancer.
Malignant tumors are distinguished from benign tumors by their progressive growth and
invasiveness. Metastasis is a characteristic of many malignant tumors (cancers) . Metastatic cells become dislodged from the main tumor, invade blood or lymphatic vessels, and travel to other tissues, where they continue to grow and to invade. In this way, tumors at one site can give rise to secondary tumors at other sites within the body.
Classification of tumors is based on the embryonic origin of the tissue from which the malignant cells are derived . Carcinomas develop from endodermal or ectodermal tissues (e.g , skin , glands) and constitute most malignant tumors, including cancers of the breast, colon, and lung. Sarcomas develop from bone and cartilage and have a much lower incidence than carcinomas. Leukemia are malignant cells of hematopoietic lineage that proliferate as individual cells, whereas lymphomas arise from malignant hematopoietic cells but grow as solid tumors.
All cancers are multifactorial in origin. They include genetic, hormonal, metabolic, physical, chemical and environmental factors. Most human cancers are spontaneous. Cancer is the second most common cause for death in developed countries, second only to cardiovascular diseases.
Any substance which increases the rate of mutation can also enhance the rate of incidence of cancer. Therefore all carcinogens are mutogens. Examples are X-ray, gamma-ray, ultraviolet ray. Some human cancers are caused by chemicals Examples nitrosamines. These may be introduced into the body by means of (a) occupation (aniline, asbestos), (b) diet (aflatoxins) or (c) lifestyle (smoking).
Tumor markers
They are substances released from the tumor cells, which could be detected in blood and therefore indicate the presence of the tumor in the body. They are useful for the following purposes:To facilitate detection of cancer. The presenceof tumor marker suggests the diagnosis.
For follow-up of cancer and to monitor theeffectiveness of the therapy and also to detectthe recurrence of the tumor.
For prognosis. Serum level of the marker mayindicate roughly the tumor load, which in turnindicates whether the disease is curable or not.
Good tumor maker should have those properties:
1. A tumor marker should be produced by tumor itself.
2. A tumor marker should not be present in healthy tissues.
3. Plasma level of a tumor marker should be at a minimum
level in healthy subjects and in benign conditions.
4. A tumor marker should be specific for a tissue .
5. Plasma level of the tumor marker should be in proportion to the both size of tumor and activity of tumor.
6. A tumor marker should be present in plasma at a detectable level, eventhough tumor size is very small.
Precautions: Tumor markers are sometimes elevated in nonmalignant conditions. Not every tumor will cause a rise in the level of its associated marker, especially in the early stages of some cancers. When a marker is used for cancer screening or diagnosis, the physician must confirm a positive test result by using imagingstudies, tissue biopsies, and other procedures.
Tumor markers can be classified as respect with the type of the molecule to:
1. Enzymes or isoenzymes (Alkaline phosphatase ALP)
2. Hormones (calcitonin)
3. Oncofetal antigens (Alpha fetoprotein AFP)
4. Carbonhydrate antigens (CA 15-3,CA 19-9, CA125)
5. Receptors (Estrogen, progesterone receptors)
Clinically Important Tumor Markers
1. Alpha Fetoprotein (AFP)
It is fetal albumin and has similarities with adult albumin. It is increased in the circulation of patients with hepatocellularcarcinoma, germ cell tumors, carcinoma of ovary and in pregnancy with fetal malformations of neural tube.
2. Carcinoembryonic Antigen (CEA)
CEA level is markedly increased in colorectal cancers. Over 50% of persons with breast, colon, lung, gastric, ovarian, pancreatic, and uterine cancer have elevated levels of CEA. CEA levels may also be elevated in inflammatory bowel disease (IBD), pancreatitis, and liver disease. Heavy smokers and about 5% of healthy persons have elevated plasma levels of CEA.
3. Beta Chain of human Chorionic Gonadotropin
Beta-HCG is synthesised by normal cells of placental villi. HCG is a glycoprotein; it has alpha and beta subunits. The alpha subunit is identical with those of FSH, TSH and LH. The beta subunitis specific for HCG. It is increased in hydatidiformmole, choriocarcinoma and germ cell tumors.4. Cancer Antigen 125 (CA-125)
CA-125 is a tumor maker for ovarian cancers. Elevatedlevels of CA-125 are also found in approximately20% of persons with pancreatic and digestive tract.
5.Calcitonin
is a hormone which decreases blood calcium concentration. Its elevated level is usually associated with medullary thyroid cancer. Calcitonin levels appear to correlate with tumor volume and metastasis. It is also useful for monitoring treatment and detecting the recurrence of cancer.
6. Prostate Specific Antigen (PSA)
It is produced by secretory epithelium of prostate gland. It is normally secreted into seminal fluid, where it is necessary for the liquefaction of semin. The PSA level is increased in prostate cancers. PSA has been found to be elevated in 60-70% patients with cancer of theprostate.
7. CA 15-3
is a marker for breast carcinoma. Elevated CA 15-3 levels are also found in patients with pancreatic, lung, ovarian, colorectal and liver cancer and in some benign breast and liver diseases. It is not useful for diagnosis. It is most useful for monitoring therapy.
8. CA 19-9
is a marker for both colorectal and pancreatic carcinoma.However elevated levels were seen in patients with hepatobiliary, gastric, hepatocellular and breast cancer and in benign conditions such as pancreatitis and benign gastrointestinal diseases. CA 19-9 levels correlate with pancreatic cancer staging.
9.Estrogen and progesterone receptors
They are used in breast cancer as indicators for hormonal therapy. Patients with positive estrogen and progesterone receptors tend to respond to hormonal treatment. Those with negative receptors will be treated by other therapies.