Extra

Summary

• CD33 a useful marker contributing to the diagnosis of aml
• less specific than myeloperoxidase and may be less sensitive than CD117
• there recognised aberrant expression by primitive lymphoid cells 10-20%
• mature cells of myeloid lineage also express CD33 so gating essential

Normal expression and function

CD33 a transmembrane receptor that recognizes sialic acid-bearing glycans it thought that CD33 functions as an inhibitory protein u8e28093 supressing signals of the innate immune system. CD33 strongly expressed on multi-lineage hematopoietic progenitors and myelomonocytic precursors; but absent from the more primitive pluripotent hematopoietic stem cells. expression of CD33 down-regulated on mature granulocytes. CD33 also expressed on human mast cells and blood basophils.

Diagnostic role

• overall around 80-90 of aml will express CD33; it tends not to be expressed in the most immature forms or those with erythroid or megakaryocytic differentiation
• high CD33 expression may correlate with npm1 mutation
• approximately 10% of b lymphoblastic or t lymphoblastic leukaemia lymphomas may aberrantly express CD33.
• CD33 can also be aberrantly expressed on some cases of plasma cell myeloma up to 25%

CD33 not expressed by mature erythrocytes platelets b-cells t-cells or nk cells. however CD33 expressed throughout myeloid maturation and so found on mature myeloid cells

Other relevant information:

CD33 has received particular attention as the molecular target of antibody-based treatment strategies in the therapy of aml. gemtuzumab ozogamicin go; mylotarg consists of a recombinant humanized anti-CD33 antibody conjugated to a derivative of the cytotoxic antitumor agent calicheamicin.

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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%	5-20%	<5%	<5%	<5%	<5%	<5%

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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