Lymphoma. Coloured scanning electron micrograph (SEM) of lymphoma cancer cells (yellow) in a lymph node. Some red blood cells are also seen. The cells are surrounded by a connective tissue capsule (purple). 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 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. Magnification: x1250 when printed at 10 centimetres wide.