Definite risk factors for non Hodgkin lymphoma

In the UK, around 12,200 cases of non Hodgkin lymphoma are diagnosed each year. This makes it the 6th most common type of cancer in adults (not counting non melanoma skin cancer). Out of every 100 cancers diagnosed, 4 are NHL (4%).

Doctors don't know the cause in most people who get non Hodgkin lymphoma. Research is going on all the time to try to find out what causes it. There are some possible risk factors on the next page in this section.

Like all cancers, non Hodgkin lymphoma is not infectious. You can't catch it from someone who has it.

People whose immune system is not working as well as it should are more likely to develop a lymphoma. Immunity can be lowered for the following reasons.

• Taking drugs to stop organ rejection after a transplant
• HIV or AIDS
• Being born with rare medical conditions which affects immunity
• Autoimmune diseases

Auto immune disease includes rheumatoid arthritis, haemolytic anaemia, coeliac disease, Sjogren's syndrome, systemic lupus erythematosus, and the skin condition psoriasis.

Past cancer treatment can affect your risk of non Hodgkin lymphoma. Some chemotherapy drugs can increase your risk of developing NHL 10 to 15 years after treatment. Having had radiotherapy in the past also increases your risk of getting NHL. People who have had radiotherapy for breast cancer or Hodgkin lymphoma have an increased risk of NHL in the area that was treated. But these are very small increases in risk, compared to the risk of not having the treatment for the original cancer.

Infection with a virus called human T cell lymphoma virus 1 (HTLV1) can increase the risk of developing NHL. This is most common in Japan and the Caribbean. Another virus called Epstein Barr virus is linked to an increased incidence of a type of NHL that is more common in Africa than Europe. It is called Burkitt's lymphoma. 

In Europe and the UK, another common bacterial infection can cause a particular type of lymphoma that starts in the stomach. The bacteria is called Helicobacter pylori. It can cause a lymphoma called MALT lymphoma. MALT stands for mucosa associated lymphoid tissue. This means that the lymphoma starts in lymphatic tissue outside the main lymphatic system. In this case, in the lining of the stomach.

An overview of the published evidence up to 2006 found that people with hepatitis C virus infection have two or three times the normal risk of NHL. Some studies have also shown a possible link between hepatitis B and NHL.

One recent study looking at people in England who were in hospital for glandular fever (infectious mononucleosis) found they had almost six times the normal risk of NHL.

Coeliac disease is a disease of the small bowel. It affects about 1 in every 250 people. People with coeliac disease have an immune reaction to gluten, a protein found in rye, wheat and barley. This reaction causes inflammation of the small bowel. For some time, coeliac disease has been a known risk factor for a rare type of lymphoma of the small bowel, called enteropathy type T cell lymphoma (ETTL). More recently, research has shown an increased risk of B cell non Hodgkin lymphomas too. The risk seems to be higher in people with poorly managed coeliac disease, and this is supported by research showing that the risk of NHL in people with a diagnosis of coeliac disease has reduced over recent decades. Sticking to a gluten free diet may help reduce your risk if you have coeliac disease. There is more information about the risk of NHL in people with coeliac disease in the questions and answers section. A recent study also suggests that people who have a brother or sister with coeliac disease may also have an increased risk of NHL.

If you have a parent, brother or sister diagnosed with NHL, you have a slightly increased risk of getting it yourself. It's about 2 to 3 times the average risk. If this seems high, do remember that the general risk of NHL is small. And most people who get NHL don't have a relative who has had it, so it isn't a major risk factor.

If you've had a melanoma, you have double the usual risk of NHL. People who have had NHL also have an increased risk of melanoma. There is some evidence that after a non melanoma skin cancer your risk of NHL is 2 or 3 times higher than in the general population. We don't know why this is. It may be because there are risk factors in common between the two cancers, such as weakened immunity. It may even be because the other condition is more likely to be picked up because you have a cancer doctor keeping a close eye on you.