Hairy cell leukemia is a rare but distinctive mature B cell tumor that constitutes about 2% of all leukemias. Because these tumors originate from B cells, they typically express B cell markers, including CD 19 and CD 20.
Clinical manifestations mostly reflect infiltration of the bone marrow, liver and spleen. Splenomegaly is particularly massive, and is the most common and sometimes only abnormal physical finding.
Flow cytometry is a study done by suspending cells in a stream of fluid and passing them by an electronic detection apparatus. The cells are then analysed using laser or impedence based technology, evaluating cell size, count and biomarker detection. Flow cytometry is used to detect hairy cell leukemia's distinctive immunophenotype staining with antibodies to CD5 (negative), CD10 (negative), CD23 (negative), CD20 (abnormally bright), CD22 (abnormally bright), CD11c (abnormally bright), CD25 (abnormally bright), CD103 (positive), and CD123 (positive).
Hairy cell leukemia derives its name from the appearance of the cancerous cells, which have fine filamentous hair-like projections.
The diagnosis can also be confirmed by viewing the cells with a special stain, known as TRAP stain, which stands for tartrate resistant acid phosphatase.
In hairy cell lelukemia, there is extensive bone marrow effacement, with replacement of hairy cells. There is interstitial or patchy infiltration of the marrow with widely spaced lymphoid cells, as well as increased amounts of reticulin fiber deposition. Because of these bone marrow changes, bone marrow aspiration leads to a "dry tap."
Cladribine, which is also known as Leukostatin, is used to treat hairy cell leukemia and multiple sclerosis. It works as a purine (adenosine) analog, inhibiting adenosine deaminase. This inteferes with the cell's ability to process DNA and destroys them.
Though cladribine is the first line treatment for hairy cell leukemia, pentostatin is equally effective in terms of response rate and remission duration. Patients taking pentostatin must have adequate renal function, as pentostatin is cleared through the kidneys and cannot be used in those with renal dysfunction.
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