Non-Hodgkin's lymphoma cells (dark purple), illustration. Lymphoma is a malignant (cancerous) growth of white blood cells (lymphocytes). White blood cells are part of the body's immune system and circulate in a clear liquid called lymph. There are many types of lymphoma depending on the cells affected. All lymphomas however, are divided into 2 types, Hodgkin's lymphoma and non-Hodgkin's lymphomas. Hodgkin's lymphoma is characterised by the presence of Reed-Sternburg cells, a giant type of macrophage. All other lymphomas are non-Hodgkin's. The cause of lymphomas are not known.