Cancer (Gk. karkinos-malignant tumour, crab) is a disease characterised by breaking down of regulatory mechanisms of normal cells, uncontrolled division of cells and the movement of proliferating cells to other parts of the body. The disease is becoming a major cause of death in the modern world as most of the infectious diseases are being controlled through vaccination and drugs. Cancer was more Common in elderly persons though its initiation begins at the quite early age. Slow changes occur at molecular and cellular levels for the latter to become cancerous.
Context
- How Cancer cells are differ from Normal Cells.
- Types Of Tumor.
- Characteristics of Cancer cells.
- Types Of Cancer
- Cause Of Cancer
1. How Is the Cancer Cells Different From Normal Cells.
Normal cells remain adhered to one another. They have a definite life span. As some old cells die, they are replaced by new cells which arise by cell n and differentiation. Both functioning of cells as well as division and differentiation of new cells are highly regulated so that the number of cells in a tissue or an organ of an adult remain almost the Whenever there is breakdown of any regulatory mechanism, a cell develops the ability to undergo uncontrolled repeated divisions forming a clone of cells. There is no adherence. The cells slip past one er forming a mass of undifferentiated cells called neoplasm (Gk, neos-new, plasma-formation) ar tumour (L. tumere-to swell). Tumour results in pressing of surrounding normal cells and tissues ino discomfort and some diruption of their functioning.
2 . Types of Tumor.
There are two types of tumor, benign and malignant. (a) Benign tumour is noncancerous or non malignant tumour which remians confined to the original position of its formation, stops increasing in size after certain growth, gets encapsulated in connective tissue so that it is unable to infiltrate into adjacent tissues, e.g., warts. It may, however, cause discomfort or pain. (b) Malignant tumour is the actual cancerous tumour which grows rapidly because the dividing cells continue proliferation, produce angiogenic factors for blood supply and become progressively invasive. Malignant tumour is not encapsulated. Its cells reach other parts of the body through blood, lymph and formation of secondaries. They form new malignant tumor in invaded parts. The phenomenon is called metastasis.
Malignant tumor prove fatal when they disrupt the function of some vital organs.
3. Characteristics Of Cancer Cells.
- The cancer cells do not require extracellular growth factors.
- The cells continue to divide repeatedly.
- There is no control over cell division.
- The cells do nt remain attached to one another but can slip past one another.
- Due to repeated divisions, cells form a large mass of undifferentiated tissue called tumour.
- Cells pass out from the tumor to new sites for forming secondary tumours. The spread of cancerous cells from one part to the other parts (through body fluids or secondaries) is called metastasis.
- Changes occur in the nucleus of cancer cells which becomes irregular, hypertrophied and granular.
- Number of lysosomes increases. There is more melanin, mucus and fat droplets.
- Mitochondrial cristae become fewer.
- Cell death is inhibited.
- Certain genes (e.g., BRCA1, BRCA2, CDH1, MLH1, PTEN) undergo mutations that reduce the ability of genetic material (DNA) to get repaired. Some of them normally function as tumour suppressor genes.
4. Types Of Cancer
On the basis of tissues affected, 200 clinically distinct cancers has been recognised. They are, however, grouped under four types- carcinoma, melanoma, sarcomas, leukemia and lymphomas.
- Carcinoma. They are cancers of epithelial tissue like skin, glands and epithelial lining of internal organs, e.g. mucous membranes, lungs, breast, pancreas, stomach, mouth, throat, cervix, prostate, etc. Carcinoma account for nearly 85% of all tumor.
- Melanoma. They are tumours arising from melanocytes of skin and other organs eg. mucosal melanoma, nodular melanoma, superficial spreading melanoma.
- Sarcomas. They are cancerous growths of mesodermal tissues like bone, cartilage, fat, etc. In human beings, sarcomas constitute only one percent of all tumor, e.g., osteoma (cancer of bone) lipoma (cancer of adipose tissue).
- Leukemias and Lymphomas. They are cancers of hematopoietic cells. In leukemia there is very high increase in number of leucocytes (200,000 to 1000000 /mm3). Immature stem cells also occur. Leukemia is also called blood cancer. Leucocytes may enter various body parts causing damage and bleeding. In lymphoma there is excessive growth of lymph nodes, spleen and lymphoid tissues (Hodgkin's disease) and formation of large number of lymphocytes.
5. Causes Of Cancer
Physical, chemical and biological agents which cause cancer are known as carcinogens. Depending upon their mode of action, carcinogens are of three types :
- Oncogenic Transformations. They change genetic material from non-oncogenic state to oncogenic state, e.g. chemicals, radiation.
- Tumour Promoters. They are actually cocarcinogens which promote tumour formation through proliferation of cells that have already undergone oncogenic transformation, e.g.., some growth factors, hormones.
- Tumour Viruses. These are viruses which are suspected to be causing cancer through oncogenic transformations. Both DNA and RNA viruses are suspected to do it.
On the basis of their nature, carcinogens are of the following types.
- Chemical Carcinogens. A number of chemicals are known to cause cancer, e.g., nitrosodimethylamine (cigarette smoke, lungcancer), 3, 4-benzopyrene (cigarette smoke, coal tar, skin and lung cancers), soot (skin and lung cancers), synthetic dyes (blood cancer), aflatoxin (liver cancer), asbestos (lung and pleural membrane cancers), mustard gas (lung cancer), vinyl chloride (liver cancer), cadmium oxide (prostate cancer), 507 dimethylstil- bestrol or DES (vaginal cancer), nickel and chromium compounds (lung cancer), 2- paphthylamine and 4-aminobiphenyl (urinary bladder), sex hormones (breast cancer), artificial sweeteners, and excessive animal protein (digestive tract cancer), etc. High fat increases risk of breast, colon, prostate and endometrial cancers. High fat raises level of bile acids which are changed into carcinogens by intestinal bacteria. Smoked foods cause stomach cancer.
- Physical or Mechanical Irritants. Repeated friction or irritation causes cancer, e.g.. jagged mouth cancer, dhoti in Maharashtrian women, Kangri in Kashmiris, smoking (mouth and lung cancer), chewing tobacco (mouth cancer).
- Radiations. UV radiations, X-rays, radioactive isotopes and other ionising radiations cause cancer, e.g., leukemia, skin cancer.
- Biological Agents. Human Papillomavirus (HPV) causes cervical cancer (Cancer of cervix).
Epstein Barr Virus produces Burkitt's lymphoma (jaw tumour) and nasopharyngeal carcinoma. Human Herpes Virus-8 forms kaposi's sarcoma (vascular neoplasm) common in AIDS patients. Hepatitis B and C viruses (HBV, HCV) seem to cause liver cancer. Helicobacter pylori, the causative agent of peptic ulcer may cause gastric carcinoma. Schistosoma haematobium produces urinary bladder cancer.
Cancer and Genes. Cell proliferation, cell differentiation and cell survival are under control of some critical regulatory genes. Mutational changes in these genes bring about oncogenic transformation.
Transposons or jumping genes are also known in certain cases to cause these changes. The changed or mutated genes are called oncogenes while the unchanged regulatory genes are generally termed as proto oncogene. Cancer associated genes are divisible into three types
- Genes that control cell division, cell growth and cell differentiation by encoding for growth factor receptors and transcription factors.These genes are sometimes called proto oncogenes.
- Genes that inhibit cell proliferation and suppress tumour formation. They are called tumour suppressor genes.
- Genes which control programmed cell death.
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