Mature B Cell Leukaemia includes a number of usually indolent leukaemias, including chronic lymphocytic leukaemia and hairy cell leukaemia.
Chronic Lymphocytic Leukaemia (CLL)
The most common leukaemia of adults. It has more common in men. China and Japan have very low incidences; the low incidence in migrant populations from these areas suggests a strong genetic component.
It is thought that exposure to specific antigens (either self or external) may lead to the development of CLL. Most tumours express a similar spectrum of antigen binding sites.
Most patients are asymptomatic at presentation. The spleen or liver may be involved; fatigue or anaemia are uncommon but possible forms of presentation. The course is indolent; less than 10% of cases transform to diffuse large B cell lymphoma. Progression to more aggressive leukaemia is rare.
In lymph nodes, CLL is characterised by a proliferation of small lymphocytes that efface the normal architecture. Mitoses are rare. In blood smears, the lymphocytes of CLL appear slightly larger than normal lymphocytes and have clumped chromatin. Many B cell antigens are identified on immunohistochemistry; these include CD20, CD5, CD79a and CD23. CD10 is usually negative.
The genetics of CLL are particularly interesting. Immunoglobulin (IG) genes are re-arranged; about half of cases are non-mutated, with over 98% of IG genes similar to germline. The remaining cases show mutation of immunoglobulin genes and are associated with an improved outcome.
B Cell Prolymphocytic Leukaemia (B-PLL)
This is a rare form of lymphocytic leukaemia (< 1%). The leukaemic cells are larger than CLL and twice the size of normal lymphocytes. The presentation is usually more rapid with B-symptoms and elevated lymphocyte counts (usually over 100). There are no specific genetic abnormalities aside from immunoglobulin gene rearrangements. Prognosis is poor and survival is < 3-4 years in most cases.
Hairy Cell Leukaemia
Hairy cell leukaemia is a rare form of lymphoid leukaemia; it is five times more common in men; it is notable for unusual cytoplasmic processes on the surface of cells giving the 'hairy' moniker. Patients present with painful splenomegaly in most cases. The prognosis of HCL is excellent with appropriate treatment; response to alpha-interferon is usually good and durable remissions can be achieved.