A risk factor is something that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, unprotected exposure to strong sunlight is a risk factor for skin cancer.

But risk factors don't tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have had any known risk factors. Even if a person with non-Hodgkin lymphoma has a risk factor, it is often very hard to know how much that risk factor may have contributed to the lymphoma.

Researchers have found several factors that may affect a person's chance of getting non-Hodgkin lymphoma. There are many types of lymphoma, and some of these factors have been linked only to certain types.

Age

Getting older is a strong risk factor for this disease, with most cases occurring in people in their 60s or older.

Gender

Overall, the risk of non-Hodgkin lymphoma is higher in men than in women, but there are certain types of non-Hodgkin lymphoma that are more common in women. The reasons for this are not known.

Race, ethnicity, and geography

In the United States, whites are more likely than African Americans and Asian Americans to develop non-Hodgkin lymphoma.

Worldwide, non-Hodgkin lymphoma is more common in developed countries, with the United States and Europe having the highest rates. Some types of lymphoma that have been linked to specific infections (described below) are more common in certain parts of the world.

Exposure to certain chemicals

Some studies have suggested that chemicals such as benzene and certain herbicides and insecticides (weed- and insect-killing substances) may be linked with an increased risk of non-Hodgkin lymphoma. Research to clarify these possible links is still in progress.

Some chemotherapy drugs used to treat other cancers may increase the risk of developing leukemia or non-Hodgkin lymphoma many years later. For example, patients who have been treated for Hodgkin disease have an increased risk of later developing non-Hodgkin lymphoma. But it's not totally clear if this is related to the disease itself or if it is an effect of the treatment.

Radiation exposure

Studies of survivors of atomic bombs and nuclear reactor accidents have shown they have an increased risk of developing several types of cancer, including leukemia, thyroid cancer, and non-Hodgkin lymphoma. Patients treated with radiation therapy for some other cancers, such as Hodgkin disease, have a slightly increased risk of developing non-Hodgkin lymphoma later in life. This risk is greater for patients treated with both radiation therapy and chemotherapy.

Immune system deficiency

People with weakened immune systems have an increased risk for non-Hodgkin lymphoma. For example, people who receive organ transplants (kidney, heart, liver) are treated with drugs that suppress their immune system to prevent it from attacking the new organ. These people have a higher risk of developing non-Hodgkin lymphoma.

The human immunodeficiency virus (HIV) can also weaken the immune system, and people infected with HIV are at increased risk of non-Hodgkin lymphoma.

Some genetic (inherited) syndromes can cause children to be born with a deficient immune system. Along with an increased risk of serious infections, these children also have a higher risk of developing non-Hodgkin lymphoma. These inherited immune deficiency diseases can be passed on to children, but people with non-Hodgkin lymphoma who do not have these inherited diseases do not pass an increased risk of lymphoma on to their children.

Autoimmune diseases

Some autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus (SLE, or lupus), and others have been linked with an increased rate of non-Hodgkin lymphoma.

In autoimmune diseases, the immune system sees the body's own tissues as foreign and attacks them, as it would a germ. Lymphocytes (the cells from which lymphomas start) are part of the body's immune system. The overactive immune system in autoimmune diseases may cause lymphocytes to grow and divide more often than normal. This may increase the risk of them developing into lymphoma cells.

Certain infections

Several types of infections may raise the risk of non-Hodgkin lymphoma in different ways.

Infections that directly transform lymphocytes

Some viruses can directly affect the DNA of lymphocytes, helping to transform them into cancer cells. The human T-cell leukemia/lymphoma virus (HTLV-1) and the Epstein-Barr virus (EBV) seem to work in this way.

Infection with HTLV-1 increases a person's risk of developing certain types of T-cell lymphoma. This virus is most common in some parts of Japan and in the Caribbean region, but is found throughout the world. In the United States, it causes less than 1% of lymphomas. HTLV-1 spreads through sexual intercourse and contaminated blood and can be passed to children through breast milk from an infected mother.

In areas of Africa where Burkitt lymphoma is common, infection with the Epstein-Barr virus (EBV) is an important risk factor for this disease. In developed countries such as the United States, EBV is more often associated with lymphomas in patients infected with HIV. It has also been linked with developing nasal T-cell lymphoma and post-transplant lymphoma.

Infections that weaken the immune system

Infection with human immunodeficiency virus (HIV), also known as the AIDS virus, commonly causes immune system deficiency. HIV infection is a risk factor for developing certain types of non-Hodgkin lymphoma, such as Burkitt lymphoma and diffuse large B-cell lymphoma.

Infections that cause chronic immune stimulation

Some long-term infections may increase the risk of lymphoma by forcing a person's immune system to be on constant alert. As more lymphocytes are made to fight the infection, there is a greater chance that genetic mistakes can occur, which might eventually lead to lymphoma.

Helicobacter pylori, a type of bacteria known to cause stomach ulcers, has also been linked to mucosa-associated lymphoid tissue (MALT) lymphoma of the stomach. The body's immune reaction to this infection increases the risk of lymphoma. The importance of this is that antibiotics can help treat some patients who have already developed lymphomas of the stomach due to H. pylori.

The hepatitis C virus (HCV) can also cause long-term infections. Recent reports have found that infection with HCV seems to be a risk factor for developing certain types of lymphoma.

Body weight and diet

Several studies have suggested that being overweight or obese may increase your risk of non-Hodgkin lymphoma. Some studies have also suggested that a diet high in vegetables may lower risk, although more research is needed to confirm this. In any event, maintaining a healthy weight and eating a healthy diet have many known health benefits outside of the possible effect on lymphoma risk.

Last Medical Review: 07/17/2009
Last Revised: 07/17/2009