Cancer is a disease in which there is uncontrolled growth of cells. Cancer is classified according to the type of cell affected in the beginning of the disease. When the cells divide to form tumor, then it is harmful to the body (but in leukemia cancer affects the normal function of the blood through abnormal division of blood cells). Growth of tumor
Normal functioning of digestive, nervous, and circulatory systems is affected because of growth of tumors. Tumors secrete certain hormones which interfere with the normal functions of the body. Stationary tumors with limited growth are usually benign (harmless/innocent).
A cell affected by cancer is called a malignant cell. When a malignant cell enters blood or lymphatic system, it moves through out the body and destroys healthy tissue. This process is called invasion and leads to metastasis, which is a very serious condition and very difficult to cure.
All malignant cells, are capable of growing blood vessels to provide nutrition to it self. This phenomenon is known as angiogenesis. The growth of tumor is effected by the process of angiogenesis.
Death of a patient because of cancer is attributed to metastatic tumors. It is observed that only 10 percent of the deaths due to cancer are attributable to primary tumor.
Recently it is found that the motility of malignant cells is more than that of normal cells. Malignant cells can easily find their way to penetrate through smaller spaces to spread out in the other parts of the body.
Normal cells in the body growth, divide, and ultimately die following a phenomenon called apoptosis. When cell deviates from this natural process, there is beginning of cancer. A malignant cell does not under go apoptosis and continues to divide and hence there is a growth of tumor.
What Causes Cancer?
Uncontrolled growth of cell can occur when there is damage or mutations to DNA, i.e. damage to the genes responsible for division of cell. Four key types of gene drive the division of cell: oncogenes and tumor suppressor genes regulate the division of cell so to say that they direct the cell to when to divide or when not to divide. Suicide genes regulate the process of apoptosis and direct the cell to kill itself under unfavorable conditions. Damages occurred to DNA are repaired by DNA-repair genes.
When functioning of oncogene and tumor suppressor gene is hampered, uncountable growth of cell occur leading to a cancer. Cancerous cell is also formed when damage to DNA is not repaired and the cell is does not commit suicide.
Carcinogens are chemicals, gases and radiations which are responsible for damaging DNA and are the main cause of cancer. Substances like tobacco, asbestos, arsenic, gases from car exhaust or fumes generated by factories, radiations like gamma and x-rays, ultraviolet are carcinogens. When we ingest carcinogens, free radicals are generated in the body which are capable of damage DNA of the cells and affect their normal functions.
Occurrence of cancer can be due to variety of reasons. Known causes of cancer, are genetic factors; lifestyle factors such as use of tobacco, alcohol, obesity, diet and nutritional status, physical activity etc; certain types of infections, and exposure to undesired environments such as chemicals and ultraviolet, x-ray radiation.