Cancer is an abnormal, continuous multiplying of cells. The cells divide uncontrollably and may grow into nearby tissue or spread to distant parts of the body. The mass of cancer cells eventually becomes large enough to produce lumps, masses, or tumors that can be detected, which can be either benign or malignant.
- 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
- 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-quarter of an inch in diameter and contains between a million to a billion cancer cells.
General Categories of Cancer
There are several general categories of cancer, with carcinomas and adenocarcinomas being the most common.
Cancers that occur in epithelial surfaces, which are the cells that form on the outer surface of the body to line or cover the body's cavities, tubes, and passageways.
Cancers that form on a glandular surface, such as the lung, breast, prostate, ovary, or kidney.
Cancers that occur in supporting structures, such as bone, muscle, cartilage, fat, or fibrous tissue.
Leukemias and lymphomas
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 this primary site of origin, such as skin, colon, or breast. For example, when cancer is found in the liver but 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.
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.
When cancer spreads to another part of the body, it is called metastatic cancer. Spreading may occur by direct extension or invasion into adjacent tissues. Systemic spread throughout the body may occur by way of the:
Arteries and veins take blood to and from all areas of the body
A network of lymphatic vessels in all areas of the body that drain and filter infectious agents