[468] Diagnostic Value of CD33 by Immunohistochemistry in Leukemia Cutis
L Ma, DSL Kim, J Cutlan, C Ross, M Lim, D Fullen. University of Michigan, Ann Arbor, MI
Background: CD33 is a glycosylated transmembrane protein that is expressed in committed myeloid precursor cells. It is down-regulated in mature granulocytes, but is maintained in monocytes/macrophages. CD33 is an important marker in immunophenotyping acute leukemias. However, the evaluation of CD33 expression has previously been restricted to flow cytometric (FC) analysis of fresh cell preparations. Recently, a new monoclonal CD33 antibody was found to react in paraffin-embedded bone marrow samples with results comparable to FC analysis. In this study, we sought to investigate the diagnostic utility of CD33 by immunohistochemistry (IHC) in cutaneous leukemic infiltrate.
Design: CD33 (clone PWS44) IHC stain was performed on formalin-fixed and paraffin-embedded skin specimens, including 23 cases of leukemia cutis (1 ALL, 7 AML-M1-3, 8 AML-M4-5, 1 AML-M6, and 6 AML-Nos) and 4 cases of inflammatory skin diseases. Twenty cases had FC data available. A cytoplasmic stain in greater than 10% of the tumor cells was considered positive. The staining was scored by two pathologists based on the percentage of immunoreactive cells (1+ = 10-50%; 2+ = >50%) and intensity (weak vs. moderate/strong).
Results: In normal skin and inflammatory skin diseases, CD33 reacted with macrophages/histiocytes. In lesions of leukemia cutis, CD33 was detected in 18 of 23 cases, with the majority (16/18, 89%) showing diffuse and moderate to strong reactivity. Sixteen of these positive cases had FC data available and the FC data correlated well with the IHC results. The two cases with weak IHC staining also had dim immunofluorescence seen with FC. Four of 5 negative cases demonstrated CD33 negativity by FC while one case had no FC data.
Result Summary | Positive cases | IHC+/FC+ | Negative cases | IHC-/FC- | | AML, Nos | 5/6 | 5 | 1/6 | 1 | | AML, M1-3 | 6/7 | 4* | 1/7 | 1 | | AML, M4-5 | 6/8 | 6 | 2/8 | 1** | | AML, M6 | 1/1 | 1 | 0/1 | 0 | | ALL | 0/1 | 0 | 1/1 | 1 | | Total | 18/23 | 16 | 5/23 | 4 | *2 cases had no FC data; **1 case had no FC data
Conclusions: CD33 monoclonal antibody labels the majority of cutaneous lesions of acute myeloid and monocytic leukemia. There is an excellent concordance between CD33 IHC results on skin acute leukemia lesions and the patient's FC data. Therefore, CD33 would be a useful diagnostic marker in evaluating cutaneous leukemic infiltrate.
Category: Dermatopathology
Tuesday, March 10, 2009 11:30 AM
Platform Session: Section E, Tuesday Morning
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