Thursday, February 24, 2011

What is cancer?

Cells are the very small units that make up all living things, including the human body. Cell growth and cell division are essential events that are involved in natural process of replacing worn-out or dying cells, and healing of wounds. Normal body cells grow, divide, and die in an orderly fashion. These normal growth, cell division and cell death are strictly controlled and regulated by the body mechanisms. Many control mechanisms exists for the control of cell growth and cell division. Genes that are located in the nucleus of the cells are the major controlling forces in the cells. This control is usually exerted through many genes that work in a co-coordinated manner. Cancer develops when these growth mechanisms are disrupted. When this happens cells begin to grow neglecting all growth control mechanisms resulting in cancer.

Cancer is not a single disease, but is a group of many related diseases that all behave in the same way in terms of cell growth and neglecting body control mechanisms for growth. Because the body does not have control over the growth of the cancer cells; they grow, invade, erode and destroy surrounding normal tissue. The human body is made up of hundreds of different kinds of cells; all of them behave differently from each other at least in some respects. There are different sets of genes for growth promotion and growth suppression. In normal healthy state the genes that promote growth, and genes that suppresses the growth are in good harmony, so that the cell growth and cell division occur only when it is needed. These growth related genes can get damaged by internal or external factors. If a growth suppressing gene is damaged the control mechanism suppressing unwanted growth may be lost. If a damage occurs in the growth promoting genes, they may lose their ability to promote cell growth, but some types of damage can actually increase the growth promoting ability of these types of genes. This may happen because the part of the gene that senses signals from the growth suppressing genes may be damaged releasing it from the control mechanisms of the growth suppressing genes. As the result of this type of damage, the genes the cell no longer pays attention to the commands of the tumor suppressor genes and continue to multiply. Every cell is programmed to die after certain number of cell divisions. Some times damage can occur to this programmed cell death gene that controls the death of the cell, thereby giving the cell the ability of immortality. If a combination ability to divide without control mechanisms and immortality are achieved that will give the cell very high chance of developing in to cancer. Most of the time only one cell accumulates all the genetic changes that are required to develop a cancer, but it soon will divide to multiple cells. Every time these abnormal cancer cells divide, the traits of lack of control by body growth mechanisms and immortality are passed to each of the daughter cells thereby, perpetuating the process of uncontrolled cell growth.

          There are many kinds of cancers that may originate from different cell types. They all may behave differently from each other, but the basic mechanism of cancer development may be similar in many cases. Many times the damage to the genes is caused by external factors like smoking, but damage to the genes may also occur as error during cells division. Many times our body is capable of recognizing the errors that occur during the cell division and can either repair or kill the cell in which the error has occurred. But some times the cell acquires ability to bypass the bodys mechanism for repairing these errors and the cell sustains the abnormality. The process of cancer development is usually a multi-step process, where the errors like the one just described accumulate.

When a cell acquires the type of error that gives them freedom from the growth control mechanism, these cellsdivide and increase in number,whereby increasing the chance of occurrence of another genetic error. External insults like smoking further damages the cells and may increase the risk of developing cancer. Some people may inherit partly damaged genes from their parents. Since their genes are abnormal to begin with, relatively few insults or errors during cell division may cause the development of cancer in these people. These people are said to have a inherited a genetic mutation that predisposes them to cancer.

          Any one of the hundreds of types of cells in the body in theory can change in to cancer, but some types of cells are more prone to be converted to cancer cells compared to rest of the cell types and subsequently the most common types of cancers can be traced to few cell types. For example the glands in the milk duct of females is highly susceptible to cancer development making breast cancer a very common form of cancer, where as it is extremely rare for the heart muscle to turn malignant. There are over 200 different types of cancer that can occur in humans. They all may behave differently from each other and may have different causes, different symptoms and may require different types of treatment.

          Normal cells stop growing once they come in contact with another cell. This phenomenon is called contact inhibition. Cancer cells tend to lose contact inhibition thereby they may grow on top of each other, or erode in to the surrounding tissues. Cells that have lost growth control usually stay or clump together to form tumors. A tumor can be non cancerous (benign) or cancerous (malignant). Benign tumors usually stay in one place in the body and do not erode in to the surrounding structures; on the other hand malignant tumors may erode in to the surrounding tissues. The malignant tumors may also erode in to the blood vessels and lymphatic vessels. After eroding, the malignant tumor cells may be showered in to the blood or lymphatic stream and may travel to different parts of the body, where they may start a secondary growth. This phenomenon of cancer cells traveling through the blood or lymphatic vessels, to form secondary growth in sites that are far away from the original tumor is called metastasis. When cells from a cancer like breast cancer spread to another organ like the lung, the cancer is still called breast cancer with lung metastasis, not lung cancer. The tissue type from which a cancer originates as well as the nature of the underlying genetic changes largely determines the behavior of that cancer. The lung metastasis from the breast cancer behaves like breast cancer and would generally respond to the same type of drugs used in the treatment of breast cancer. Again the type of cell from which the cancer originated will generally determine the speed at which it grows, and its resistance to treatment, but at the same cancers arising from the same tissue may often show marked variations in behavior. For example breast cancer in one person may grow very slowly over a period of several years, where as in another person with breast cancer, which is arising from the same cell type may have very aggressive course and may progress in few weeks.

          Cancers cause harm and damage to the body in number of ways. The very size of the tumor can interfere with nearby organs, or ducts, which carry important enzymes, causing pain or other symptoms. For example obstruction of the pancreatic duct may cause severe diarrhea, jaundice and colicky abdominal pain. The tumor may produce some chemical that may suppress the appetite, thereby leading to marked weight loss. Some types of cancers like lymphoma may cause fever, chills and night sweats. Some types of cancers like prostate cancer may co-exist with the patient for several years without causing any symptoms.