What is Cancer? | Types of Cancer | Differences between Cancer Cells and Normal Cells | Cancer Symptoms
Cancer Treatment | How Cancer Arises, Causes and Risk Factors | “Drivers” of Cancer | Types of Medical Imaging
WHAT IS CANCER
According to the National Cancer Institute, Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues.
Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.
When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors.
Many cancers form solid tumors, which are masses of tissue. Cancers of the blood, such as leukemias, generally do not form solid tumors.
Cancerous tumors are malignant, which means they can spread into, or invade nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor.
Unlike malignant tumors, benign tumors do not spread into, or invade nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life-threatening.
Cancer is a genetic disease—that is, it is caused by changes to genes that control the way our cells function, especially how they grow and divide.
Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun.
Metastatic Cancer: the process by which cancer cells spread to other parts of the body. For example, breast cancer that spreads to and forms a metastatic tumor in the lung is metastatic breast cancer, not lung cancer. Metastatic cancer cells and cells of original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.
TYPES OF CANCER
There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer starts in cells of the lung, and brain cancer starts in cells of the brain. Cancers also may be described by the type of cell that formed them, such as an epithelial cell or a squamous cell.
You can search the National Cancer Institute’s website for information on specific types of cancer-based on cancer’s location in the body or by using our A to Z List of Cancers. We also have collections of information on childhood cancers and cancers in adolescents and young adults. Here are some categories of cancers that begin in specific types of cells.
Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when viewed under a microscope. Carcinomas that begin in different epithelial cell types have specific names: Adenocarcinoma is cancer that forms in epithelial cells that produce fluids or mucus. Tissues with this type of epithelial cell are sometimes called glandular tissues. Most cancers of the breast, colon, and prostate are adenocarcinomas.
Basal cell carcinoma is cancer that begins in the lower or basal (base) layer of the epidermis, which is a person’s outer layer of skin.
Squamous cell carcinoma is cancer that forms in squamous cells, which are epithelial cells that lie just beneath the outer surface of the skin. Squamous cells also line many other organs, including the stomach, intestines, lungs, bladder, and kidneys. Squamous cells look flat, like fish scales, when viewed under a microscope. Squamous cell carcinomas are sometimes called epidermoid carcinomas.
Transitional cell carcinoma is cancer that forms in a type of epithelial tissue called transitional epithelium, or urothelium. This tissue, which is made up of many layers of epithelial cells that can get bigger and smaller, is found in the linings of the bladder, ureters, and part of the kidneys (renal pelvis), and a few other organs. Some cancers of the bladder, ureters, and kidneys are transitional cell carcinomas.
Soft tissue sarcoma forms in soft tissues of the body, including muscle, tendons, fat, blood vessels, lymph vessels, nerves, and tissue around joints.
Sarcomas are cancers that form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).
Osteosarcoma is the most common cancer of the bone. The most common types of soft tissue sarcoma are leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma, lip sarcoma, and dermatofibrosarcoma protuberans.
Cancers that begin in the blood-forming tissue of the bone marrow are called leukemias. These cancers do not form solid tumors. Instead, large numbers of abnormal white blood cells (leukemia cells and leukemic blast cells) build up in the blood and bone marrow, crowding out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to its tissues, control bleeding, or fight infections.
There are four common types of leukemia, which are grouped based on how quickly the disease gets worse (acute or chronic) and on the type of blood cell cancer starts in (lymphoblastic or myeloid). Our page on leukemia has more information.
Lymphoma is cancer that begins in lymphocytes (T cells or B cells). These are disease-fighting white blood cells that are part of the immune system. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body.
There are two main types of lymphoma:
Hodgkin lymphoma – People with this disease have abnormal lymphocytes that are called Reed-Sternberg cells. These cells usually form from B cells.
Non-Hodgkin lymphoma – This is a large group of cancers that start in lymphocytes. The cancers can grow quickly or slowly and can form from B cells or T cells.
Multiple myelomas is cancer that begins in plasma cells, another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumors in bones all through the body. Multiple myelomas are also called plasma cell myeloma and Kahler disease.
Melanoma is cancer that begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color). Most melanomas form on the skin, but of the brain and spinal cord tumors. These tumors are named based on the type of cell in which they formed and where the tumor first formed in the central nervous system. For example, an astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. Brain tumors can be benign (not cancer) or malignant (cancer).
Other Types of Tumors:
Germ Cell Tumors
Germ cell tumors are a type of tumor that begins in the cells that give rise to sperm or eggs. These tumors can occur almost anywhere in the body and can be either benign or malignant.
Our page of cancers by body location/system includes a list of germ cell tumors with links to more information.
Neuroendocrine tumors form from cells that release hormones into the blood in response to a signal from the
nervous system. These tumors, which may make higher-than-normal amounts of hormones, can cause many different symptoms. Neuroendocrine tumors may be benign or malignant.
Brain and Spinal Cord Tumors
There are different types:
Carcinoid tumors are a type of neuroendocrine tumor. They are slow-growing tumors that are usually found in the gastrointestinal system (most often in the rectum and small intestine). Carcinoid tumors may spread to the liver or other sites in the body, and they may secrete substances such as serotonin or prostaglandins, causing carcinoid syndrome.
Visit the National Cancer Institute’s online page on gastrointestinal carcinoid tumors for more information.
Related Resources, Cancer Staging, Tumor Grade, Pathology Reports, Metastatic Cancer, Common Cancer Myths and Misconceptions.
DIFFERENCES BETWEEN CANCER CELLS AND NORMAL CELLS
Cancer cells differ from normal cells in many ways that allow them to grow out of control and become invasive. One important difference is that cancer cells are less specialized than normal cells. That is, whereas normal cells mature into very distinct cell types with specific functions, cancer cells do not. This is one reason that, unlike normal cells, cancer cells continue to divide without stopping.
In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing or that begin a process known as programmed cell death, or apoptosis, which the body uses to get rid of unneeded cells.
Cancer cells may be able to influence the normal cells, molecules, and blood vessels that surround and feed a tumor—an area known as the microenvironment. For instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumors with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumors.
Cancer cells are also often able to evade the immune system, a network of organs, tissues, and specialized cells that protects the body from infections and other conditions. Although the immune system normally removes damaged or abnormal cells from the body, some cancer cells are able to “hide” from the immune system.
Tumors can also use the immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can actually keep the immune system from killing cancer cells.
According to the American Cancer Society, the following Are Signs and Symptoms of Cancer:
Unexplained Weight gain or loss with no known reason
Change in bowel habits or bladder functions
Sores that do not heal
White patches inside the mouth or white spots on the tongue
Unusual bleeding or discharge
Thickening or lump on or under the skin, the breast or other parts of the body
Indigestion or trouble swallowing, problems with eating, such as discomfort after eating
A hard time swallowing
Changes in appetite
A recent change in a wart or mole or any new skin change
Nagging cough or hoarseness
Skin changes, such as a new mole or a change in an existing mole
Breast changes, such as a change in size or shape of the breast or nipple, Change in texture of breast skin
Hoarseness or cough that does not go away
Difficult or painful urination
Unexplained night sweats
Unusual bleeding in the stool, discharge in the urine and vaginal bleeding
Feeling weak or very tired
Most often, these symptoms are not due to cancer. They may also be caused by benign tumors or other problems. If you have symptoms that last for a couple of weeks, it is important to see a doctor so that problems can be diagnosed and treated as early as possible.
Usually, early cancer does not cause pain. If you have symptoms, do not wait to feel pain before seeing a doctor.
Cancer can cause many different symptoms
The signs and symptoms listed above are the more common ones seen with cancer, but there are many others that are not listed here. If you notice any major changes in the way your body works or the way you feel – especially if it lasts for a long time or gets worse – let a doctor know. If it has nothing to do with cancer, the doctor can find out more about what’s going on and if needed, treat it. If it is cancer, you’ll give yourself the chance to have it treated early, when treatment works best. To learn more about symptoms for specific cancer, visit National Cancer Institute online.