Almost every review begins "CLL is the commonest leukemia in the western world". I wonder who first wrote that sentence? And is it true?
Traditionally, it is believed that the great German pathologist Rudolf Virchow coined the term leukemia. It just means white blood. In fact the first description of leukemia (and I shall stick to the American spelling because it saves a key stroke) was by John Hughes Bennett, the Englishman who was Professor of Medicine at Edinburgh, a Scottish University, and who beat Virchow to the punch by 6 weeks. You can actually trace an even earlier case of what was probably leukemia from the writings of the Parisian doctor, Armand Velpeau, eighteen years earlier in 1827. Both Virchow and Bennett studied in Paris before they made their discoveries.
There are lots of causes of increased white cells in the blood that are not leukemia. What makes a leukemia is the fact all the cells are the children of a single parent. They are monoclonal - genetically identical members of the same clone. In CLL they are also lymphocytes. A lymphocyte is one of the 5 types of white blood cell (the others are monocyte, neutrophil, eosinophil and basophil). Lymphocytes are members of the immune system and are further subdivided into T cells (derived from the Thymus), B cells (derived from the Bone marrow) and NK cells (it stands for Natural Killer). CLL cells are B-lymphocytes.
(Immunologists will correct me here, because the B originally stood for the Bursa of Fabricius, an organ near the cloaca of a chicken which modifies fowl B cells. But mice and men don't have one, so B is for Bone Marrow was adopted instead.)
B lymphocytes are the ones that are destined to make antibody. Antibodies are chemicals made by the body to react specifically with something that is foreign to the body. (I am not going to explain antibodies in this posting - I will get to them at a later date.)
CLL is sometimes called a tumor of B cells, but that is confusing because tumor means swelling and not every case of CLL has a swelling. It's medical shorthand for a growth.
When I trained, doctors went in for euphemisms a lot. Instead of calling something a cancer it was called a growth or a neoplasm or a tumor or a mitotic lesion, or just a lesion. It is not simply a matter of avoiding telling the patient the truth; there is also the matter of precision. To most doctors cancer is the lay-term for carcinoma. Cancer is Latin for a crab - it is one of the signs of the Zodiac. Carcinoma is Greek for crab. The Patricians speak Greek; the Plebians talk Latin. A carcinoma is a malignant neoplasm of epithelial tissue. Blood is not an epithelial tissue, so we get uncomfortable when patients talk about a cancer of the blood.
Neoplasm just means newly formed or moulded or grown (Greek again). So in lay terms a neoplasm is a new growth. It isn't necessary cancer; it could be a benign (good) or a malignant (nasty) growth. A lesion refers to any kind of tissue damage (it comes from the Latin for hurt). A mitotic lesion is one that is characterised by mitoses. Mitosis is the mechanism by which cells duplicate their chromosomes and divide, so a mitotic lesion is a hurt in which cell division is prominent - in other words a cancer. Strictly speaking leukemias should be called sarcomas. A sarcoma is a malignant growth of a non-epithelial tissue. Epthelial tissue is what covers the outside of the body. But you have to remember that the lining of the gut is the outside of the body; outside but inside if you see what I mean.
We used to have the term lymphosarcoma. This was another term coined by Virchow. In the Bible we read of God bringing all the animals to Adam in the Garden of Eden for him to give them names. Virchow was very like Adam, very good at naming things. Lymphosarcoma became to be used for a particular form of neoplasm of lymphocytes and is now no longer used. W use the term lymphoma instead to refer to neoplasms of lymphocytes and strictly speaking CLL is a form of lymphoma, though by convention we call liquid tumors leukemias and solid tumors lymphomas. When CLL is mainly solid it is known as small lymphocytic lymphoma or SLL. Often patients talk of having CLL/SLL. That usually means that they have seen an oncologist who is more comfortable dealing with lymphomas than leukemias.
"Chronic" is also from the Greek and has to do with time. We talk about Acute leukemias which happen quickly and Chronic leukemias that happen slowly.
So CLL is the slow malignant growth of one of the white blood cells - the one known as a B-lymphocyte that should have been in the business of making antibodies.