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Cancer is one of the most important non-infectious or non-communicable diseases.
“Cancer is referred to as an ailment characterised by an unrestrained growth of abnormal cells which if untreated and unchecked eventually kills the patient.”
In India nearly four lakhs of people are affected by cancer every year. Out of them two lakhs of people die. It is mainly due to late detection. Many people are not aware of the early symptoms of this disease.
What is Cancer?
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The growth of multicellular animals occurs due to addition of new cells. The old or existing cells divide by mitosis to form new cells. This division is controlled and regulated by some factors. Sometimes, due to unknown reasons, some cells divide in abnormally faster rate to form a lump.
This lump increases rapidly causing ulcers. It causes serious complications in the body. These abnormal cells first destroy the organ and then the whole body. These cells utilize the total food of the body. So the affected person becomes weak, looses his weight and ultimately dies. The tumors, enclosed in connective tissue are called benign tumor and when the tumors grow, it is called as malignant.
Types of Cancer:
Cancer can be divided into different types:
1. Sarcoma:
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The cancer which occurs in muscles, cartilages, bones, blood vessels, connective tissues are known as sarcoma.
2. Carcinoma:
This type of cancer originates from skin or cells which lines the internal organs.
3. Lymphoma:
It is the cancer of lymph glands and lymph nodes.
4. Leukemia:
It occurs in blood forming organs, specially the bone marrow. It is found that no organ of body and no species is free from cancer.
Causes of Cancer:
The real cause of cancer is not yet known.
The following aspects can be attributed to the cause of cancer:
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1. Excessive smoking has been found to be associated with lung cancer, cancer in urinary bladder, mouth, throat, larynx etc.
2. Chewing of tobacco, betel nuts etc. are believed to be the cause of cancer in mouth, throat, oesophagus etc.
3. A large number of dyes, chemicals, heavy metals can cause cancer.
4. Ionic radiations like X-ray, gamma ray etc. can cause cancer.
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5. Alcohol is thought to be the cause of cancer in stomach, liver, gall bladder etc.
6. Pollutants like chemicals, smoke, dust may be responsible for cancer. Though the exact cause of cancer is not known, the above described substances are mutagens which can cause mutation in genes. The mutant genes have no control over normal functioning of the cell. So it may lead to cancer.
Sites of Cancer:
Though cancer can develop at any part or organ of the body, it mostly develops in some organs like liver, alimentary canal, larynx, pharynx, tongue, lips, gall bladder, lungs, uterus, urinary bladder, lymph nodes, bones etc.
Primary Symptoms of Cancer:
1. Presence of any persistent lump or thickening of tissues in lip, tongue or breast.
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2. Any wound that does not heal.
3. Unusual bleeding or discharge of blood.
4. Persistent indigestion, difficulty in swallowing.
5. A regular change in bowel movements.
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6. Rapid change in rate of growth, colour and form of mole or wart.
7. Change in the voice.
8. Unusual loss of weight of the body.
How Cancer Spread?
Cancer spreads inside the body rapidly and infects other organs, called metastasis:
(i) Cancer cells grow through the walls of blood vessels.
(ii) Cancer cells are carried by the blood stream to other parts of the body.
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(iii) Cancer cells pass through lymphatic vessels and lymph glands.
(iv) Cancer cells spread from tissues to tissues.
Behaviour of Cancerous Cells:
Normal cells of the body have a control over the division. The controlling factor is present in the DNA. The DNA directs the cells to divide and stops the division when not required. In cancerous cells the controlling factor is not present, probably due to mutant genes. Due to absence of controlling factor, the mitosis continues uncontrolled and forms cancer. It is believed that these cells carry certain cancer causing genes, called oncogens. These oncogenes remain inactive. Certain conditions initiate these genes to multiply and destroy the normal controlling factor of the cells.
Suspected Involvement of Virus in Cancer:
The role of virus is strongly suspected now. Some retrovirus, which causes tumor may be involved in this process. It is known that these viruses have RNA as genetic material. These RNA have the capacity to integrate with the host DNA. By the process of “reverse transcriptase”, these RNA make copy of the DNA.
This DNA acts as viral oncogene. The viral oncogenes may interact with the oncogenes of the cell, called proto-oncogenes and take control of the cell function. The DNA, which have been transcribed from viral RNA, transcribe back the viral RNA through normal transcription processes forming large number of new retroviruses.
Treatment of Cancer:
Cancer is curable, if it is detected at the early stages. The patient enjoys full life without recurrence of the disease.
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Cancer is treated in three ways:
(i) Surgery:
Some of the infected organs are removed from the body by surgery: Example-Uterus, breast etc.
(ii) Radiotherapy:
The affected organs are irradiated to kill the cancerous cells and prevent them from spreading.
(iii) Chemotherapy:
Strong chemicals are used to kill the cancerous cells and isolate these cells from other organs. Sometimes all these three methods are applied to cure cancer. This dreaded disease can be cured fully, if it is detected at the preliminary stage. So social consciousness should be developed for early detection.
Oncogenes:
Oncogenes (Gk. Onkos meaning cancer) were initially identified as genes carried by viruses that cause transformation of their target cells. A major class of Oncogenes, the oncogenes present in acute transforming retroviruses, has homologues in animal genomes; these cellular counterparts are called Proto- oncogenes.
Proto-Oncogenes:
Proto-oncogenes participate in normal cell function, and in certain cases, a mutation or aberrant activation of a Proto- oncogenes causes tumour formation. So far trans membrane proteins to transcription factors.
Viral Oncogenes:
Transformation represents a gain-of-function in which a Proto- oncogene is activated either because of its acquisition by a retrovirus (this generates a viral oncogene or v-onc) or its activation by mutation or by association with new regulatory sequences due to recombination, leading to its expression where it is usually not expressed or an over expression in the tissue of its usual expression (this generate cellular oncogenes or (c-onc). Oncogenic development results from either increased expression of the oncogene or an alteration in the activity of the oncoprotein. Oncogene in such cases therefore is dominant over its Proto- oncogene counterpart.
Tumour Supressor Genes:
There are a group of genes whose inactivation (loss-of -function) by mutation, including deletion leads to tumour formation; these are known as Tumour Suppressor Genes. These genes usually impose some restriction on the cell cycle or cell growth.
Therefore a loss-of- function for such genes is tumorigenic. In such cases, tumour development is recessive to normal development, and both the alleles must be inactivated by mutation or deletion to allow oncogenesis.
