Hodgkin lymphoma is caused by a change (mutation) in the DNA of a type of white blood cell called B lymphocytes, although the exact reason why this happens is not known.

The DNA gives the cells a basic set of instructions, such as when to grow and reproduce. The mutation in the DNA changes these instructions so that the cells keep growing. This causes them to multiply uncontrollably.

The abnormal lymphocytes usually begin to multiply in one or more lymph nodes in a particular area of the body, such as your neck or groin. Over time, it is possible for the abnormal lymphocytes to spread into other parts of your body, such as your bone marrow, spleen, liver, skin and lungs.

Who is most at risk?

While the cause of the initial mutation that triggers Hodgkin lymphoma is unknown, a number of factors can increase your risk of developing the condition:

• having a medical condition that weakens your immune system, such as HIV
• having medical treatment that weakens your immune system – for example, taking medication to suppress your immune system after an organ transplant
• being previously exposed to the Epstein-Barr virus (EBV), a common virus that causes glandular fever
• having previously had non-Hodgkin lymphoma, possibly because of treatment with chemotherapy or radiotherapy

Hodgkin lymphoma isn't infectious and isn't thought to run in families. Although your risk is increased if a first-degree relative (parent, sibling or child) has had lymphoma, it is not clear if this is because of an inherited genetic fault or lifestyle factors.

Hodgkin lymphoma can occur at any age, although most cases are diagnosed in people in their 20s or 70s. The condition is slightly more common in men than women.