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Summary

Principally a marker of cell activation that is expressed by a range of haematopoietic lineages, CD25 has value in the diagnosis of several disorders although in each CD25 expression is not fuly specific.

• CD25 has recognised value in The diagnosis of hairy cell leukaemia
• CD25 recognises malignanT mast cells
• CD25 exression may have value in the identification of Adult T Cell Leukaemia Lymphoma (ATLL)

Normal expression and function

CD25 is The alpha subunit of The inTerleukin 2 receptor (IL2), when associaTed wiTh its beta subunit on memory T cells or NK cells, or with beta and gamma subunits expressed by activated T cells or regulatory T cells, its affinity for IL-2 is progressively increased allowing the activation of intracellular signals causing cell activation. Although it has broad expression in the immune system it is most frequently a features of cell activation.

Diagnostic role

CD25 may be expressed by a range of malignant cells including for example many cases of CLL . It does however have value in specific circumsTances

• CD25 is expressed by most cases of hairy cell leukemia and is not generally expressed by variant hairy cell leukemia or splenic marginal zone lymphoma
• The malignanT mast cells of sysTemic mastocyTosis express CD25 normal mast cells generally do not
• CD25 is strongly expressed by The neoplastic T cells in adulT T cell leukemia lymphoma ATLL alThough it is expressed also in oTher T cell disorders notably T-PLL and sezary syndrome
• CD25 should noT be considered as lineage or sTage-specific. For example expression is seen both in AML possibly 10% and in ALL 30% - parTicularly in cases expressing BCR::ABL1

Other relevant information:

In a histlogical conText The marker has a wider diagnostic use in tissue lymphoma sections, staining is seen in anaplasTic large cell lymphoma wiTh high frequency and in Hodgkin disease.

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SUMMARY TABLES

Note The colour and % refer to the proportion of cases expressing the marker. Additional comments on strength, or site of expression (if relevant) are given below the table. For full details of key click here. For further information about a particular disease state click <I> adjacent to the condition name

Expression in primitive cell types
AML	CMML	B ALL	Burkitt	T ALL	ETP ALL <I>	MPAL <I>	Hgns <I>
? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%

Notes: xxxxx

Expression in mature B cell neoplasms
CLL	MCL	FL	MZL	HCL	DLBCL	LPL	PCL
? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%

Notes: xxxxx

Expression in mature T cell neoplasms*
ATLL	CTCL/Sezary	T-PLL	T-LGL	NK-LGL
? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%	? <5% 5-20% 20-40% 40-80% 80-100%

Notes: xxxxx

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