Extra

Summary

CD33 a useful marker contributing to the diagnosis of AML, but is less specific than myeloperoxidase and may be less sensitive than CD117.

The molecule is expressed by normal maturing myeloid cells, and there is recognised aberrant expression by primitive lymphoid cells (10-20%).

Normal expression and function

CD33 a transmembrane receptor that is thought to function as an inhibitory protein supressing signals of the innate immune system. It is strongly expressed on multi-lineage hematopoietic progenitors and also on myelomonocytic precursors (although generally less strongly than CD13). Expression is absent from the more primitive pluripotent hematopoietic stem cells and CD33 is down-regulated on mature granulocytes, human mast cells, and blood basophils.

Diagnostic role

• Overall around 80-90% of AML cases express CD33; although the marker tends not to be expressed the least mmature forms, as well as those with erythroid or megakaryocytic differentiation. High CD33 expression may correlate with NPM1 mutation
• Approximately 10% of B or T lymphoblastic leukaemias and lymphomas may aberrantly express CD33 as well as up to 25% of myeloma cases
• CD33 not expressed by mature cells of erythroid, platelet, B-cells T-cells or NK-cell lineage
• CD33 is expressed throughout myeloid maturation and is found on mature myeloid cells, though less strongly on cells of monocytic lineage

Other relevant information:

CD33 has received particular attention for its role as the molecular target of antibody-based treatment strategies in the therapy of AML.

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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>
style="width: 12.5%; background: #004466; color:white"|80-100%*	<5%	5-20%	5-20%	5-20%	20-40%**	20-40%**	style="width: 12.5%; background: #004466; color:white"|80-100%***

Notes: Expression in B-ALL may be associated with BCR::ABL1 expression

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

Notes: *Expression is not always seen in MCL but may have high intensity **Strong expression intensity is expected in HCL

summary tables expression by acute leukaemias and by haematogones poss pro-b all poss early pre-b all poss pre-b all poss b all poss pro-t all poss mature-t all hi aml freq haemato-gones notes *in all the expression of CD33 more likely in b-lineage but also seen in t-all

• • in aml CD33 expressed in around 80 of cases ***in haematogones expression of CD33 frequent

expression by b-lymphoproliferative disorders rare cll rare pll rare mcl rare fl' rare hcl rare hclv rare mzl rare lpl poss pcs

• CD33 occasionally expressed in mature lymphoid malignancies more frequently in b cell types

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

Notes: CD25 has characteristically strong expression on ATLL, but other T-LPD also express the marker less strongly

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summary tables expression by acute leukaemias and by haematogones poss pro-b all poss early pre-b all poss pre-b all poss b all poss pro-t all poss mature-t all hi aml freq haemato-gones notes *in all the expression of CD33 more likely in b-lineage but also seen in t-all

• • in aml CD33 expressed in around 80 of cases ***in haematogones expression of CD33 frequent

expression by b-lymphoproliferative disorders rare cll rare pll rare mcl rare fl' rare hcl rare hclv rare mzl rare lpl poss pcs

• CD33 occasionally expressed in mature lymphoid malignancies more frequently in b cell types