A risk factor is anything that increases a person's chance of getting a disease such as cancer. Risk factors can be classified as genetic (inherited), lifestyle-related, or environmental.

However, most patients with non-Hodgkin lymphoma have no known risk factors. It’s also important to note that having one or more risk factors doesn't mean that a person will develop this cancer. Age is the greatest factor for this disease, with most cases occurring among those in their 60s.

Genetic Risk Factors

Several genetic diseases can cause children to be born with an abnormal or deficient immune system. In addition to developing serious infections due to reduced immune defenses, they also have an increased risk of developing non-Hodgkin lymphoma during childhood or as young adults. How this happens is discussed in the section "Do We Know What Causes Non-Hodgkin Lymphoma?".

Although these congenital (present at birth) immune deficiency diseases can be passed on to children, people with non-Hodgkin lymphoma who do not have these inherited diseases do not pass an increased risk of lymphoma to their children.

Lifestyle-Related Risk Factors

Examples of lifestyle-related risk factors for some cancers include exposing skin to strong sunlight, a diet high in fat and low in fruits and vegetables, and habits such as smoking and excessive drinking of alcohol.

Lifestyle-related factors such as these do not strongly affect a person's risk of developing non-Hodgkin lymphoma. However, being obese may increase your risk of non-Hodgkin lymphoma.

Environmental Risk Factors

Environmental risk factors are influences in our surroundings, such as radiation, chemicals, and infections.

Radiation: Survivors of atomic bombs and nuclear reactor accidents 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 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.

Chemicals: Some studies have suggested that chemicals such as benzene and certain herbicides and insecticides (weed- and insect-killing substances) are associated with an increased risk of non-Hodgkin lymphoma. Recent studies have found that this is not certain, and research to clarify this issue is still in progress.

Some chemotherapy drugs used to treat other cancers can increase the risk of developing leukemia or non-Hodgkin lymphoma many years later; however, a direct cause and effect relationship has not yet been definitely established. For example, patients who have been treated for Hodgkin disease have an increased risk of later developing non-Hodgkin lymphoma. This may be related to the disease itself or may be an effect of the treatment.

Immune deficiency: Patients with transplanted organs (kidney, heart, liver) and some other conditions like rheumatoid arthritis are treated with drugs that interfere with their immune system to prevent it from attacking the new organs. This effect on the immune system carries a significant risk to the patient of developing non-Hodgkin lymphoma. The exact risk depends on which drugs and at what doses they are used.

Infections: Infection with human immunodeficiency virus (HIV), also known as the AIDS virus, is an increasingly common cause of immune system deficiency. HIV infection is a risk factor for developing certain types of non-Hodgkin lymphoma.

Infection with the human T-cell leukemia/lymphoma virus (HTLV-1) increases a person's risk of developing certain types of T-cell non-Hodgkin lymphoma. This virus is most common in some parts of Japan and in the Caribbean region. In some areas of Japan, it is responsible for about half of the non-Hodgkin lymphoma cases. In the United States, it causes less than 1% of lymphomas. HTLV-1 belongs to the same family of viruses as HIV. Like HIV, it spreads through sexual intercourse and contaminated blood and can be passed to children through breast milk.

In areas of Africa where Burkitt lymphoma is common, infection with the parasite that causes malaria and with the Epstein-Barr virus (EBV) are important risk factors for this disease. EBV is also associated with lymphomas in developed countries, particularly in patients infected with HIV.

Scientists have recently found that a type of bacteria, Helicobacter pylori, known to cause stomach ulcers, can also cause lymphomas of the stomach. The body's immune reaction to this infection increases the risk of non-Hodgkin lymphoma. The most important consequence of this recent discovery is that antibiotics can be helpful in treating some patients who have already developed lymphomas of the stomach.

Revised 6-04