[1597] Utility of CD117 Immunohistochemistry in Evaluation of Myelodysplastic Syndrome

Xiaolin Wu, Jiehao Zhou, Shanxiang Zhang, Mehdi Nassiri, Magdalena Czader. Indiana University, Indianapolis, IN

Background: In myelodysplastic syndrome (MDS), the evaluation of bone marrow histology complements assessment of cytologic features and provides additional information relevant for diagnosis and prognosis. Immunohistochemical stains, primarily CD34, are increasingly used to facilitate the identification of blasts. This is particularly helpful in cases with hemodilute marrow aspirate smears. Various authors suggested that CD117 immunostain can complement CD34. However, there are no systematic studies on CD117 expression in MDS by immunohistochemistry. We have evaluated the utility of CD117 stain in MDS and compared its expression to blast differential counts (BL%) and CD34 positivity (CD34%).
Design: 60 MDS samples (52 patients) were studied: 9 RA, 3 RARS, 16 RCMD, 6 RAEB-1, 12 RAEB-2, 3 MDS, NOS, 1 5q- syndrome and 2 therapy-related MDS. CD34 and CD117 antibodies (DAKO, Carpinteria, CA) and autostainer DAKO-Plus were used. 1000 cells were counted at 100x oil immersion objective. CD117 was scored separately in blasts, promyelocytes, erythroid and mast cells. Percentages of CD117+ immature cells (CD117%) and CD34% were compared to BL%. Differences were considered diagnostically significant if resulted in a change of final diagnosis. CD34+ and CD117+ clusters and aggregates were recorded per 10 HPF (400x). Wilcoxon rank and Spearman correlation test were used.
Results: CD117% showed positive correlation with BL% (r 0.571). However, diagnostically significant differences were seen: 6 cases (10%) showed decreased CD117% in comparison to BL% (difference range 2-10%, original diagnoses RAEB-1 and RAEB-2; diagnosis change to RAEB-1 and RCMD), and 1 case had an increased CD117%. In most cases, results did not change significantly regardless whether CD117+ promyelocytes and/or erythroid precursors were excluded. There were 13 cases of mast cell hyperplasia. However, mast cells were identified easily and excluded from the counts.
Ten cases showed significantly higher and 6 lower CD34% as compared to BL%. In 18 cases, the difference between CD34 and CD117 positivity was diagnostically significant. The numbers of CD117+ aggregates and clusters were lower than those obtained by CD34 immunostain.
Conclusions: CD117 immunostain showed a tendency to underestimate numbers of immature cells. These results are likely due to a combination of factors including true antigen loss, poor antigenicity and uneven distribution of CD117+ cells. In most cases, counting all CD117+ immature cells did not significantly influence the results and simplified the evaluation. The significant variability between CD34 and CD117 counts has to be further explored.
Category: Hematopathology

Tuesday, March 20, 2012 9:30 AM

Poster Session III # 235, Tuesday Morning

 

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