This blood cancer is relatively common and has many different subtypes.

Non-Hodgkin lymphoma (NHL) is a type of blood cancer.

NHL typically develops in the lymph nodes. Lymph nodes make immune cells that help the body fight infections.

NHL begins when a type of white blood cell, called a lymphocyte, becomes abnormal.

The abnormal lymphocytes grow out of control and divide into more abnormal lymphocytes, which eventually form tumors.

There are several different types of NHL, which are classified based on how slow-moving or aggressive the disease is and what kind of lymphocytes are abnormal.

Prevalence of Non-Hodgkin Lymphoma

NHL accounts for about 3 to 4 percent of all U.S. cancer cases, according to the American Cancer Society.

It's the seventh most-common type of cancer in the United States.

In 2014, there were about 584,000 people in the United States living with non-Hodgkin lymphoma, according to the Leukemia & Lymphoma Society.

There is roughly one new case of non-Hodgkin lymphoma each year for every 5,000 people living in the United States, says the National Cancer Institute. That means about 64,000 new cases will be diagnosed in 2015.

Roughly 2.1 percent of people in the United States will be diagnosed with non-Hodgkin lymphoma at some point.

Non-Hodgkin Lymphoma Risk Factors

A risk factor is something that affects your chance of getting a disease.

There aren't a lot of known risk factors for non-Hodgkin lymphoma. Many people who develop the disease have no obvious risk factors.

Known or suspected risk factors for non-Hodgkin lymphoma include:

Exposure to certain bacteria or viruses: Researchers think that non-Hodgkin lymphoma may be associated with certain bacteria or viruses that weaken the immune system.

Among these are HIV (the virus that causes AIDS), Epstein-Barr virus (which causes mononucleosis), human T-lymphocytotrophic virus (HTLV), and Helicobacter pylori, a bacterium that causes stomach ulcers.

Age: Getting older increases your risk of non-Hodgkin lymphoma.

The disease is most commonly diagnosed in adults over the age of 60.

Sex: Most types of NHL are more common in men than in women.

Chemicals: Exposure to certain chemicals, including benzene and some weed- and insect-killing chemicals, has been linked to an increased risk of NHL.

Chemotherapy drugs used to treat other cancers may also increase the risk of NHL years later.

Radiation exposure: People treated with radiation for other cancers have a slightly higher risk of developing NHL years later.

Hodgkin lymphoma: If you were treated for Hodgkin lymphoma, you have a slightly higher risk of developing NHL at some point in your life.

This may be due to the risks associated with chemo and radiation.

Non-Hodgkin Lymphoma Survival

Doctors often discuss a patient's prognosis, or outlook, for different cancers by mentioning the five-year survival rate, or the percentage of patients who live at least five years after their cancer is diagnosed. (Some people live much longer.)

The five-year survival rate for non-Hodgkin lymphoma is about 70 percent, according to the National Cancer Institute.

Certain factors, such as the stage of the cancer (how far it has spread) at the time of diagnosis, affect a person's likelihood of survival.

Non-Hodgkin Lymphoma in Children

Non-Hodgkin lymphoma is the fifth most-common pediatric cancer in the United States. Each year, about 800 new cases of NHL are diagnosed in children under the age of 15.

Most children who get NHL don't have any obvious risk factors for the disease.

Non-Hodgkin lymphoma is rare in children, but those with congenital (present at birth) immune system problems may have a higher risk of developing NHL.

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