There are several atypical forms of hairy cell leukemia that share many features with classic hairy cell leukemia (HCL) but which have a different immunophenotype.

Features which may be present:

(1) splenomegaly

(2) anemia and/or thrombocytopenia with bone marrow infiltration

(3) circulating "hairy cells" but these may be present in small numbers


Classic immunophenotype:

(1) CD25 positive

(2) CD11c positive

(3) CD103 positive

(4) HC2 positive

(5) CD20 positive


Variants forms are usually but not always CD25 negative. They may or may not show staining for:

(1) CD10

(2) CD103

(3) CD11c

(4) HC2


Subtypes include:

(1) Japanese variant

(2) prolymphocytic-like

(3) variant with CD25 and HC2 negativity


It is important to recognize these forms since they may not respond to standard HCL therapies.

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