Definition of Cancer
Cancer has been defined in a number of different ways. This definition is the best of all:
Cancer is a popular generic term for malignant neoplasms,
a great group of diseases of three main causes, occurring in all human and animal populations and arising in all tissues composed of potentially dividing cells.
The basic characteristic of cancer is the transmissable abnormailty of cells that is manifested by reduced control over growth and function leading to serious adverse effects on the host through invasive growth and metastases .
To help you understand this medical jargon, let us take this definition and break it down into its parts.
The word cancer comes from the Latin for crab, probably because of the way a cancer adheres to any part that it seizes upon in an abstinate manner like the crab. It is a popular, generic term because the actual medical term for cancer is neoplasia which, from the Greek, means new formation. Cancers are new growths of the cells in our bodies. Cells are the basic unit of life - each of us has trillions of them. Our cells help us carry out all functions of life - from the beating of the heart to the throwing of a football. Malignant neoplasms refers to the fact that the new growth has virulent or adverse properties that it may display in the body. Through expression of these properties, it can cause destruction of major organs, and in some cases, life threatening disturbances in body function.
...a great group of diseases of three main causes, occurring in all human and animal populations and arising in all tissues composed of potentially dividing cells.
Every cell in the body has the potential to form a new growth. Indeed, this is not a problem just of humans, but in fact all living organisms (plants and animals) are susceptible to cancer, simply because all living organisms are made up of cells. Cells are dynamic - they are constantly in the process of making decisions about what they want to do next. The decision to grow is one such major decision. Cells grow by dividing in half, such that one cell will become two, and two become four (these new cells are called daughter cells), etc... Normally, there are very strict rules as to when a cell can grow or not. These rules are set down by a variety of players, including all of the cells around it, various hormones in the body, and various external factors to which the cell may respond. One important example is growth of our bones from infancy to early adulthood. Cells at the ends of the bones are given very regulated orders to divide and make more bone so that we can get taller.
The cell basically is set loose to divide without its normal control. When this happpens, the cell continues to divide, eventually forming a new growth that is what we know as a tumor or neoplasia. When this division reaches the point where the number of daughter cells is 1,000,000,000 (one billion!), it is detectable by conventional examination methods, like a chest x-ray or a rectal examination.
The basic characteristic of cancer is the transmissable abnormailty of cells that is manifested by reduced control over growth and function leading to serious adverse effects on the host through invasive growth and metastases.
When a cell is set loose from normal control, it becomes what is known as transformed. Basically, the cell no longer looks like its neighbors in terms of its shape, size, and its internal components. This transformed property is conferred upon all of the daughter cells. That is , all subsequent cells that arise from that initially transformed cell will also look different and grow in an uncontrolled manner. This is the transmissable nature of cancer - once one cell becomes cancerous, all cells that arise from this abnormal cell will also take on this characteristic.
As stated above, 1,000,000,000 is the minimum number of cancer cells that can be detected by physical and radiologic examination. Nonetheless, much of the adverse effects that a cancer incurs upon the body may have already occured at this point. These are due to the malignant properties that the uncontrolled cells take on as they divide. They gain these properties because rapid growth causes more mistakes to be made in the DNA of the cell - the chemical in the cell that allows it to carry out is normal functions. When mistakes are made, the cell gets reprogrammed to take on new functions and to lose some that it had before. It now may become more motile, as if it were a white blood cell, or it may lose the ability to remain in contact with its neighborring cells. When these events take place, the malignant cells may leave the local site and travel in the body fluids to a distant organ. This process is known as metastases. Dissemination of cancer cells throughout the body will allow secondary tumors or neoplasms to be established in other organs. It this widespread growth which leads to organ failure by invasive growth and destruction of normal cells with subsequent compromise of function.