Extra

Summary

Principally a marker of cell activation that is expressed by a range of haematopoietic lineages, The expression of CD25 has value in the diagnosis of several disorders although in each case expression is not fully specific and the level of expression may be key to diagnosis

• High levels of CD25 are typical in hairy cell leukaemia
• CD25 is expressed by many malignant mast cells
• CD25 expression is useful in the identification of Adult T Cell Leukaemia Lymphoma (ATLL)

Normal expression and function

CD25 is one subunit (alpha subunit) of the interleukin 2 receptor (IL2), CD25 has broad expression in the immune system but is most frequently a features of cell activation. CD25 associates with a beta subunit on memory T cells and NK cells or with beta and gamma subunits on activated or regulatory T cells to increase its affinity for IL-2 and allowing the activation of intracellular signals that cause cell activation.

Diagnostic role

CD25 may be expressed by a range of malignant cells; for example many cases of CLL, but detection has value in specific circumstances

• CD25 is expressed by most cases of hairy cell leukemia (HCL) with less expression by related disorders such as splenic marginal zone lymphoma
• The malignant mast cells of systemic mastocytosis express CD25, while normal mast cells generally do not
• CD25 is strongly expressed by the neoplastic T cells in adult T cell leukaemia lymphoma (ATLL) although it is expressed also in other T cell disorders notably T-PLL and Sézary syndrome
• CD25 should may also be expressed in AML (around 10%) and in ALL (around 30% and particularly in cases expressing BCR::ABL1)

Other relevant information:

In a histlogical context CD25 has a wider diagnostic use staining anaplastic large cell lymphoma, and 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>
5-20%	<5%	<5%	<5%	<5%	<5%	<5%	<5%

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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Summary Tables

1. expression by acuTe leukaemias and by haemaTogones file rare pro-b all rare early pre-b all rare pre-b all rare early b all rare pro-T all rare maTure-T all poss aml* rare haemaTo-gones

• expression is reporTed To be associaTed wiTh BCR-ABL1

2. expression by b-lymphoproliferaTive disorders poss cll poss pll mod mcl mod fl hi hcl poss hclv rare mzl freq lpl rare pcs considered a sTrong indicaTor of hcl allowing discriminaTion from hclv and mzl