What Is Cancer?
Cancer describes a group of diseases in which abnormal cells grow out of control.
The American Cancer Society estimates the 5 most deadly cancers for 2020 in the U.S. are:
How Many Types of Cancer Are There?
There are more than 100 types of cancer that can affect almost every part of the body.
Types of cancer are usually named for the organs or tissues in which the cancers form, such as lung cancer that starts in cells of the lung, and pancreatic cancer that starts in cells of the pancreas.
Cancers are also named by the type of cells that form them. Some categories of cancers that begin in specific types of cells include:
- Carcinomas are the most common type of cancer, formed by epithelial cells that cover the inside and outside surfaces of the body.
- Adenocarcinoma forms in epithelial cells that produce fluids or mucus. Most cancers of the breast, colon, and prostate are adenocarcinomas.
- Basal cell carcinoma begins in the lower (basal) layer of the outer layer of skin (epidermis).
- Squamous cell carcinoma (also called epidermoid carcinoma) forms in epithelial cells that lie just beneath the outer surface of the skin and that line many organs, such as the stomach, intestines, lungs, bladder, and kidneys.
- Transitional cell carcinoma forms in a type of epithelial tissue called transitional epithelium, or urothelium, which is made up of many layers of epithelial cells found in the linings of the bladder, ureters, and part of the kidneys, and other organs.
- These are cancers that form in soft tissues of the body, including muscle, tendons, fat, blood vessels, lymph vessels, nerves, and tissue around joints.
- Osteosarcoma is the most common cancer of bone.
- The most common types of soft tissue sarcoma are leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma, liposarcoma, and dermatofibrosarcoma protuberans.
- These are cancers that begin in the blood-forming tissue of the bone marrow.
- They do not form solid tumors but instead large numbers of abnormal white blood cells build up in the blood and bone marrow.
- Multiple myelomas
- Also called plasma cell myeloma and Kahler disease, these cancers begin in plasma cells, a type of immune cell.
- These cancers begin in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color).
- Brain and spinal cord tumors
- Other types of tumors
- Germ cell tumors begin in the cells that give rise to sperm or eggs.
- Neuroendocrine tumors form from cells that release hormones into the blood in response to a signal from the nervous system.
- Carcinoid tumors are a type of neuroendocrine tumor that is usually found in the gastrointestinal system, often in the rectum and small intestine.
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