Lymphoma is a cancer of the white blood cells, starting in solid areas of immune cells.
This is an astoundingly complex process, involving many types of WBC's and supporting cells. To understand lymphoma, it helps to have some understanding of how the immune system works, and what type of cells normally do that work. A cell may become cancerous at any point along it's development, accounting for the many types of blood cell cancers. While there is ultimately just one type of RBC and platelet, there are normally several main types, and many subtypes, of WBC's. The main types are lymphocytes, neutrophils, monocytes, eosinophils, and basophils.