The term "cancer" refers to a group of diseases in which cells have uncontrolled growth and spread throughout the body. It is difficult to imagine anyone who has not heard about this disease. Most people have been affected because either a loved one, a friend, or even they themselves are cancer survivors.
It is therefore important for everyone to have a basic understanding about the nature, diagnosis, causes, prevention, and treatment of cancer.
This article will help you find answers to many of your questions about the nature, causes, and prevention of cancer. You can learn about the following topics:
What is cancer?
How is cancer detected and diagnosed?
What causes cancer?
What is the link between genes and cancer?
What is cancer prevention?
Different Kinds of Cancer
Cancer can originate almost anywhere in the body.
Carcinomas , the most common types of cancer, arise from the cells that cover external and internal body surfaces. Lung, breast, and colon are the most frequently diagnosed carcinomas in the United States.
Sarcomas are cancers arising from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue, and muscle.
Lymphomas are cancers that arise in the lymph nodes and tissues of the body's immune system.
Leukemias are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream.
Scientists use a variety of technical names to distinguish among the many different types of carcinomas, sarcomas, lymphomas, and leukemias. In general,these names are created by using different prefixes that stand for the name of the cell type involved. For example, the prefix "osteo" means bone, so a cancer arising in bone is called an osteosarcoma. Similarly, the prefix "adeno" means gland, so a cancer of gland cells is called adenocarcinoma--for example, a breast adenocarcinoma.
Loss of Normal Growth Control
Cancer starts when there is a loss of normal growth control. In normal tissues, the rates of new cell growth and old cell death are kept in balance. In cancer, this balance is disrupted. This disruption can result from uncontrolled cell growth or loss of a cell's ability to undergo "apoptosis." Apoptosis, or "cell suicide,"is the mechanism by which old or damaged cells normally self-destruct.
Example of Normal Growth
To illustrate what is meant by normal growth control, consider the outermost layer of the skin. The thin outer layer of normal skin, called the epidermis, is roughly a dozen cells thick. Cells in the bottom row of this layer, called the basal layer, divide just fast enough to replenish cells that are continually being shed from the surface of the skin. Each time one of these basal cells divides, it produces two cells. One remains in the basal layer and retains the capacity to divide. The other migrates out of the basal layer and loses the capacity to divide. The number of dividing cells in the basal layer therefore stays the same.
The Beginning of Cancerous Growth
During the development of skin cancer, the normal balance between cell division and cell loss is disrupted. The basal cells now divide faster than is needed to replenish the cells being shed from the surface of the skin. Each time one of these basal cells divides, the two newly formed cells will often retain the capacity to divide, thereby leading to an increase in the total number of dividing cells.
Invasion and Metastasis
Cancers are capable of spreading through the body by two mechanisms: invasion and metastasis. Invasion refers to the direct migration and penetration by cancer cells into neighboring tissues. Metastasis refers to the ability of cancer cells to penetrate into lymphatic and blood vessels, circulate through the bloodstream, and then invade normal tissues elsewhere in the body.
The gradual increase in the number of dividing cells creates a growing mass of tissue called a "tumor" or "neoplasm." If the rate of cell division is relatively rapid, and no "suicide" signals are in place to trigger cell death, the tumor will grow quickly; if the cells divide more slowly, tumor growth will be slower. But regardless of the growth rate, tumors ultimately increase in size because new cells are being produced in greater numbers than needed. As more and more of these dividing cells accumulate, the normal organization of the tissue gradually becomes disrupted.