Lymphomas develop because of changes in the genes of a lymphocyte (a type of white blood cell). These changes alter how the cell grows and divides or may prevent it dying when it normally should do. Often more than one change happens in the genes before a lymphoma develops.

We now know a lot about the gene changes in different types of lymphoma. In most cases, however, no one really knows what makes the changes happen. This is probably because lymphomas are caused by lots of different things that each affect the genes in a small way. Scientists sometimes call this the ‘multi-hit theory’.

There are some things that are known to increase the risk of developing lymphoma (often called ‘risk factors’). These are things that have been linked with certain types of lymphoma or are seen more often in people with lymphoma. They are not a cause on their own. Known risk factors for lymphoma include:

a close relative having lymphoma
previous treatment for cancer
getting older.
problems with the immune system
certain infections