CD34

Summary

Often regarded as a marker of primitive phenotype, CD34 is expressed by many cases of ALL (around 50%) and slightly fewer cases of AML around (40%). CD34 is also expressed by regenerating cells in marrow. It is particularly expressed by regenerating B lymphocytes (haematogones), but is generally absent from mature haematopoietic cells, lower expression in AML may be seen in APL, and in ALL may suggest Burkitt lymphome.

Normal expression and function

CD34 is a membrane protein that is likely to play a role in the retention of cells within the stem cell niche where it may also contribute to their subsequent maturation. CD34 is acquired at the stage of pluripotent stem cells and is retained by committed stem cells before being lost as the cells mature. CD34 is also expressed by mast cells and by some non-haematopoietic cells particularly endothelial cells.

Diagnostic role

• CD34 is commonly used to identify the primitive nature of early lymphoid or myeloid cells i.e. blast cells of ALL and AML
• Rare very primitive cases of acute leukaemia may be identified solely through their expression of CD34 and CD45
• CD34 is also expressed by regenerating cells in marrow and also by regenerating haematogones so caution is necessary in interpretation in regenerating marrows

Other relevant information:

Histopathologists often use CD34 to demonstrate the number of primitive cells in bone marrow trephine biopsies e.g. in the assessment of primitive cell number in myelodysplaia. However, a range of other cell types in bone marrow also express CD34 in marrow, and these include vascular endothelial cells and mast cells.

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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	BL	T ALL	ETP ALL	MPAL	Hgn
40-80%*	5-20%**	40-80%*	5-20%	40-80%*	40-80%*	40-80%*	40-80%***

Notes: * In acute leukaemias expression is frequent but not absolute and tends to be expressed on less more mature forms ** expression on CMMl is infrequent and may be abberant, but may also indicate transformation to an acute leukaemia, *** Haematones typically express CD34, but it is lost on more mature haematogones

Expression in mature B cell neoplasms
CLL	MCL	FL	MZL	HCL	DLBCL	LPL	PCL
<5%	<5%	<5%	<5%	<5%	<5%	<5%	<5%

Expression in mature T cell neoplasms*
ATLL	CTCL/Sezary	T-PLL	T-LGL	NK-LGL
<5%	<5%	<5%	<5%	<5%

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