Haematological cancers most often begin in the bone marrow where blood is produced. Stem cells in the bone marrow develop into white blood cells, red blood cells, or platelets. Blood cancers occur when uncontrolled growth of abnormal blood cells overtakes the development of normal blood cells and interferes with the regular functions of these cells. Blood cancers fall into three categories: leukaemia, lymphoma, and myeloma.
Leukaemias are blood cell cancers; some leukaemias are fast growing, while others develop slowly. Lymphoma occurs when lymphocytes (infection-fighting white blood cells) develop abnormally and become cancerous. These multiply and aggregate in lymph nodes and other tissues. Among common lymphomas are Hodgkin lymphoma, non-Hodgkin Lymphoma, AIDS-related lymphoma, and primary central nervous system (CNS) lymphoma. Myeloma is a cancer that occurs in plasma cells. Normal plasma cells produce antibodies that fight disease and infection. However, when abnormal plasma cells develop, they interfere with antibody production and lead to reduced immunity.
A solid tumor is an abnormal mass of tissue that usually does not contain cysts or liquid areas. Solid tumors may be benign (not cancer), or malignant (cancer). Solid tumor types are named according to the type of cell they originate from. Examples of solid tumors are sarcomas, carcinomas, and lymphomas. Leukaemias (cancers of the blood) generally do not form solid tumours.
The word tumor does not always imply cancer. In discussing tumors that are malignant (cancerous), however, the term solid tumor is used to distinguish between a localized mass of tissue and leukemia.