What is Cancer ?

The Definition of Cancer

Cancer is a condition in which cancer cells spread to other areas of the body.

Cancer can occur anywhere in the body. It is composed of trillions upon trillions of cells. Normally, human cells grow and multiply (through a process called cell division) to form new cells as the body needs them. Cells can become old or damaged and then die.

Sometimes, this process can break down and damaged or abnormal cells grow and multiply in a way that is not normal. Tumors are a mass of tissue that is formed when these cells become damaged or abnormal. Tumors can be cancerous or not cancerous (benign).

Cancerous tumors spread into, or invade, nearby tissues and can travel to distant places in the body to form new tumors (a process called metastasis). Cancerous tumors may also be called malignant tumors. Many cancers form solid tumors, but cancers of the blood, such as leukemias, generally do not.

The benign tumors are not able to spread into or invade nearby tissues. Most benign tumors don’t grow back after being removed. Cancerous tumors can sometimes grow back. However, benign tumors can grow to be very large. Certain tumors can have serious consequences or even be fatal.

There are differences between cancer cells and normal cells

In many ways, cancer cells are different from normal cells. Cancer cells are an example of this:

• They will not grow if there are no signals to tell them. Normal cells can only grow when they are given such signals.
• Do not ignore signals telling cells to stop dividing (programmed cell death or apoptosis)
• Invade nearby areas and spread to other parts of the body. Normal cells cease to grow when they come into contact with other cells. Most normal cells don’t move around the body.
• Tell blood vessels to grow towards tumors. These blood vessels provide oxygen and nutrients to tumors and also remove any waste products.
• hide from the immune system. Normally, the immune system eliminates abnormal or damaged cells.
• The immune system can be tricked into believing that cancer cells will grow and stay alive. For instance, some cancer cells convince immune cells to protect the tumor instead of attacking it.
• accumulate multiple changes in their chromosomes, such as duplications and deletions of chromosome parts. Some cancer cells have twice the normal number ofchromosomes.
• Different types of nutrients are required by cancer cells than in normal cells. Some cancer cells also make energy from nutrients differently than normal cells. This allows cancer cells to grow faster.

These abnormal behaviors are often so important that cancer cells can’t live without them. This fact has been exploited by researchers who have developed therapies to target cancer cells’ abnormalities. For example, some cancer therapies prevent blood vessels from growing toward tumors, essentially starving the tumor of needed nutrients.

How does cancer develop?

Certain genetic changes can cause cancer. These are the fundamental physical units that make up inheritance. The DNA chromosomes, which are long strands of densely packed DNA, are the basic units of inheritance.

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.

It is possible to have genetic changes that cause cancer.

• Several errors can occur when cells divide.
• The environment can cause DNA damage, such as from chemicals in tobacco smoke or ultraviolet rays. (Our Cancer Causes and Prevention section has more information.)
• they were inherited from our parents.

Normally, cells with damaged DNA are removed by the body before they become cancerous. As we age, our bodies’ ability to eliminate cancerous cells decreases. This is why you are at greater risk for cancer later in your life.

Every person is different and each cancer has its own unique genetic makeup. As cancer grows, more changes are likely to occur. Different cells in the same tumor may have different genetic mutations.

Types of Genes That Cause Cancer

The genetic changes that contribute to cancer tend to affect three main types of genes–proto-oncogenes, tumor suppressor genes, and DNA repair genes. These genetic changes are often called “drivers” for cancer.

Proto-oncogenes play an important role in cell division and growth. These genes can become cancer-causing genes (or even oncogenes) if they are altered in certain ways. This allows cells to grow and live when they shouldn’t.

The regulation of cell division and growth is also controlled by tumor suppressor genes. Certain mutations in tumor suppressor genes can cause cells to divide uncontrollably.

The DNA repair genes are responsible for fixing damaged DNA. Cells with mutations in these genes tend to develop additional mutations in other genes and changes in their chromosomes, such as duplications and deletions of chromosome parts. These mutations can cause cancerous cells.

Scientists have discovered that certain mutations are common in all types of cancer. Now there are many cancer treatments available that target gene mutations found in cancer. A few of these treatments can be used by anyone with a cancer that has the targeted mutation, no matter where the cancer started growing.

When cancer spreads

Metastasis is when cancer cells travel through the bloodstream or lymph system to form new tumors (metastatic cancers) in other areas of the body. Metastatic cancer is the same type as primary cancer.

Metastatic cancer is a form of cancer that spreads from the original site where it was formed to another part of the body. Metastasis is the process by which cancer cells spread from one part of the body to another.

Metastatic cancer is the same as primary cancer in that it has the same name and uses the same type cancer cells. Metastatic breast cancer is, by definition, a metastatic cancer in which a metastatic tumor forms in the lung.

Metastatic cancer cells look similar to original cancer cells when examined under a microscope. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.

Sometimes, metastatic cancer treatment can prolong the life expectancy of patients. Other cases of metastatic cancer treatment have a primary goal to stop the spread of the disease or relieve the symptoms. Metastatic cancers can cause serious damage to the body’s ability to function, and metastatic disease is responsible for most deaths from cancer.

Tissue changes that are not cancerous

Some changes in the body’s tissue are not cancerous. However, some tissue changes can become cancerous if not treated. These are examples of tissue changes that aren’t cancerous but should be monitored in certain cases as they may become cancerous.

• HyperplasiaThis happens when cells in a tissue multiply more quickly than normal, and extra cells are formed. Under a microscope, however, cells and how the tissue is organized look normal. Hyperplasia can result from several conditions or factors, including chronic irritation.
• Dysplasia Hyperplasia is a more severe condition than dysplasia. Dysplasia also causes an accumulation of extra cells. The cells are abnormally shaped and the organization of the tissues is altered. The likelihood of cancer is higher for cells and tissues that are more abnormal. While some types of dysplasia need to be treated or monitored, others don’t. A dysplasia example is an abnormal mole, also known as a Dysplastic nevus() that forms on your skin. Although most people do not get melanoma from a dysplastic nevus, it can become melanoma.
• Carcinoma in situ This is a more severe condition. It is often called stage 0 cancer. However, the abnormal cells don’t invade surrounding tissue in the same way as cancer cells. They are treated because some carcinomas may develop into cancer.

ypes for Cancer

There are over 100 types of cancer. The organs and tissues that the cancers develop are often named after the types of cancer. Lung cancer begins in the lung and brain cancer in the brain. The type of cell that made cancers, such as epithelial cells or squamous cells, can also be used to describe them.

NCI can be searched online for specific types of cancer by locating the cancer in the body. You can also use our A to Z List Of Cancers. Information on cancers of children and adolescents as well as young adults is also available.

These are the types of cancers that start in certain cells:

Carcinoma

Carcinomas are the most prevalent type of cancer. These cancers are caused by epithelial cells. They cover both the outside and inside of the body. Many types of epithelial cell exist, and they often look like columns when examined under a microscope.

Different epithelial cell types can be affected by carcinoma. They have their own names.

Adenocarcinoma refers to cancer that develops in epithelial cells, which produce fluids and mucus. These epithelial cells are often called glandular tissues. Adenocarcinomas are the most common form of cancer in the prostate, breast and colon.

Basal cell carcinoma refers to a form of cancer that starts in the basal (or base) layer of the epidermis. This is the outer layer of the skin.

Squamous cell carcinoma refers to a type of cancer that develops in squamous (epithelial cells located just below the outer skin surface) squamous cells. Many other organs are also lined by squamous cells, such as the stomach, intestines and bladder. When viewed under a microscope, squamous cells appear flattened, similar to fish scales. Sometimes, epidermoid carcinomas can be called squamous cell carcinomas.

A type of epithelial tissue known as transitional epithelium or urothelium is where you will find transitional cell carcinoma. This tissue is composed of multiple layers of epithelial cell that can grow and shrink and is found in the linings and ureters of the bladder and kidneys, as well as the renal pelvis and other organs. Transitional cell carcinomas can occur in the kidneys, bladder, ureters and kidneys.

Sarcoma

Soft tissue sarcoma occurs in the soft tissues of your body. This includes muscle, tendons and fat.Credit: TereseWinslow

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, the most common bone cancer, is the most prevalent. Leiomyosarcoma and Kaposi sarcoma are the most common soft tissue sarcomas.

Our page on soft tissue sarcoma has more information.

Leukemia

Cancers that begin in the blood-forming tissue of the bone marrow are called leukemias. These cancers don’t form solid tumors. Instead, abnormal white blood cells, also known as leukemia cells or blast cells, build up in the bloodstream and bone marrow and crowd out normal blood cells. Low levels of normal blood cells can make a person’s body less able to obtain oxygen, control bleeding and fight infection.

There are four types of leukemia. They are classified based on how rapidly the disease progresses (acute or chronic), and the type of blood cells the cancer begins in (lymphoblastic, myeloid). Chronic forms of leukemia are slower growing than acute forms.

Our page on leukemia has more information.

Lymphoma

Lymphoma refers to cancer that starts in lymphocytes (T or B cells). These white blood cells are part of the immune defense system and are able to fight off disease. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body.

There are two types of lymphoma.

Hodgkin lymphoma–People with this condition have abnormal lymphocytes, which are known as Reed-Sternberg cell. These cells are usually formed from B cells.

Non-Hodgkin lymphoma is a type of lymphoma that starts in lymphocytes. These cancers can develop quickly or slowly, and can be formed from either B cells or T cells.

Our page on lymphoma has more information.

Multiple Myeloma

Multiple myeloma is cancer that begins in plasma cells, another type of immune cell. Myeloma cells are abnormal plasma cells that build up in bone marrow. They can then form tumors throughout the body. Multiple myeloma can also be called plasma cell myeloma or Kahler disease.

Our page on multiple myeloma and other plasma cell neoplasms has more information.

Melanoma

Melanoma occurs when melanocytes (specialized cells that produce melanin, the pigment that gives skin its color) develop from cancer cells. Melanomas most often form on the skin. However, melanomas can also develop in other pigmented tissues such as the eye.

More information is available on our pages about skin cancer and intraocular melanomas.

Brain and Spinal Cord Tumors

There are many types of spinal cord and brain tumors. These tumors are named according to the type of cell they originated from and the location where it first formed in the central nerve system. An example of an astrocytic brain tumor is found in astrocytes (star-shaped brain cells), which help maintain nerve cells health. Brain tumors may be benign (not cancerous) or malignant.

More information is available on our pages about brain and spine cord tumors in adult and children.

Other types of tumors

Germ Cell Tumors

Germ cell tumors can be a form of cancer that develops in the cells that produce sperm and eggs. These tumors can develop anywhere on the body, and they can be 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

Neuroendocrine tumors are formed when cells release hormones into blood in response to signals from the nervous system. These tumors can produce higher than normal levels of hormones and cause many symptoms. Neuroendocrine tumors can be benign or malignant.

Our definition of neuroendocrine tumors has more information.

Carcinoid Tumors

Carcinoid tumors can be classified as a neuroendocrine type. These tumors are slow-growing and are most commonly found in the small intestine and rectum. 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.