Overview of Cancer
It is the nature of cells to divide and increase their number in a process called mitosis. Normal cells divide to replace those lost, or to repair injuries only, then stop dividing.
Cancer is an abnormal, continuous multiplying of cells. The cells divide uncontrollably and may grow into adjacent tissue or spread to distant parts of the body. The mass of cancer cells eventually become large enough to produce lumps, masses, or tumors that can be detected, which can be benign or malignant:
- benign tumors:
- are not cancerous
- can usually be removed
- do not come back in most cases
- do not spread to other parts of the body, and the cells do not invade other tissues
- malignant tumors:
- are cancerous
- can invade and damage nearby tissues and organs
- metastasize (cancer cells break away from a malignant tumor and enter the bloodstream or lymphatic system to form secondary tumors in other parts of the body)
The smallest cancer that can be detected by examination, x-ray, or scan is slightly less than one-fourth of an inch in diameter and contains between a million to a billion cancer cells.
There are several general categories of cancer, with carcinomas and adenocarcinomas being the most common:
- Carcinomas - are cancers that occur in epithelial surfaces - the cells that form the outer surface of the body to line or cover the body's cavities, tubes and passageways.
- Adenocarcinomas - are cancers that form on a glandular surface, such as the lung, breast, prostate, ovary, or kidney.
- Sarcomas - are cancers that occur in supporting structures, such as bone, muscle, cartilage, fat, or fibrous tissue.
- Leukemias and lymphomas - are cancers that occur in blood cell elements.
Brain cancers, nerve cancers, melanomas, and certain testicular and ovarian cancers do not fall into a general category.
Cancers begin in a single cell, and that cell is the site of the primary cancer. The cancer is named for the primary site of origin, such as skin, colon, or breast. For example:
- When cancer is found in the liver that originated in the colon it is called colon cancer that has metastasized to the liver, not liver cancer.
- Liver cancers are those that originated from a liver cell. If it spreads to the lung, it is still liver cancer, not lung cancer.
- When cancer spreads to the regional lymph nodes, those nodes are said to contain metastatic cancer. (Cancers that originate in the lymph cells of a node are called lymphomas.)
Cancer can spread from its original location to other parts of the body.
- Spreading may occur by direct extension or invasion into adjacent tissues.
- Systemic spread throughout the body may occur by way of the:
- blood system - arteries and veins take blood to and from all areas of the body
- lymphatic system - a network of lymphatic vessels in all areas of the body that drain and filter infectious agents
- cerebrospinal fluid
When cancer spreads to another part of the body, it is called metastatic cancer.
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