Our body consists of a set of cells visible only through a microscope. These cells divide periodically and regularly to replace old or dead ones, and maintain the integrity and proper functioning of various organs.
The process of cell division is regulated by a series of control mechanisms that tell the cell when to start to divide and when to remain static. When these control mechanisms are altered in a cell, it and its descendants initiate an uncontrolled division, which eventually will lead to a tumor or nodule.
When cells that constitute the tumor do not have the ability to invade and destroy other organs, they are called benign tumors. But when these cells grow uncontrollably besides suffering new changes and acquire the ability to invade surrounding tissues and organs (infiltration), and to move and grow in other parts of the body (metastasis), they are termed as malignant tumor or cancer.
There are many types of cancer namely skin cancer, breast cancer, blood cancer or leukemia etc. The evolution of each type of cancer is subject to many factors that will interact with each other. These factors vary depending on both the tumor and the patient.
The development of certain diseases such as obesity, heart disease and cancer depend greatly on the lifestyle of the individual. Smoking increases the chances of developing lung or mouth cancer.
Excessive alcohol consumption also increases the probability of occurrence of liver and stomach cancer.
75-80% of the time, cancer is caused due to the action of external agents acting on the body, causing alterations in the cells. In the other 20-25% of cases, the exact mechanisms by which cancer develops and produces are not known. It is thought to be due to spontaneous mutations of the genes or by the action of some external factor that has not yet been identified.
Scientific and technological advances of recent years have provided new insights into the emergence, development and growth of cancer. These advances, in practice, resulted in improved cancer treatments and reduced side effects from them. For example, surgery performed today can treat malignant tumors effectively without causing harm to the body organs of the patient.
The main forms of treatment are surgery, chemotherapy and radiotherapy. The effectiveness of these treatments has not been proven scientifically. At present, there are no drugs that can cure cancer or even prevent the formation of cancerous cells in the body.