A person with lymphoma has abnormal cells in the lymph nodes or spleen that multiply out of control. These cells, called lymphocytes, are part of the immune system, which fights infection. The cells can form tumors and spread to other parts of the body.

Many forms of cancer are on the decline in the US, but lymphomas have become more common. The two main types of lymphoma are Hodgkin's disease and non-Hodgkin lymphoma.