[1506] OCT-2 and BOB.1 Expression in Acute Leukemias

Michael T Schmidt, Chelsea Hayes, Sumire Kitahara. Cedars-Sinai Medical Center, Los Angeles, CA

Background: Lineage assignment for acute leukemias can occasionally be challenging when the defining lineage markers are negative and the remaining alternative is to make a diagnosis of acute leukemia of ambiguous lineage. We had encountered cases where the leukemia was negative for CD19, CD22, CD79a and PAX5 (as well as T and myeloid markers), but were positive for OCT-2 and BOB.1 only. In this study, we investigate the specificity of the B-cell associated transcription factor OCT-2 and its co-activator BOB.1, which have been shown to be expressed in various mature B-cell neoplasms, in acute leukemias to determine whether these markers could be useful in lineage determination for B-ALL when all other markers are negative.
Design: 80 cases of treatment naïve newly diagnosed acute leukemias from bone marrow biopsies were retrieved and immunohistochemically stained with OCT-2 and BOB-1. 32 cases of AML, 37 cases of B-ALL, 9 cases of T-ALL and 2 cases of leukemias of ambiguous lineage as defined by WHO criteria made up our study population. Only cases which showed blast populations comprising greater than 30% of marrow elements on core biopsy were included for evaluation. OCT-2 and BOB.1 were considered positive if nuclear staining was observed and expression was seen in greater than 10% of the blasts. The staining intensity ranged from weak to strongly positive.
Results: In AMLs, 22 of 32 (69%) cases showed OCT-2/BOB.1 co-expression. Individually, 23 of 32 (72%) cases showed OCT-2 expression and 28 of 32 (88%) cases showed BOB.1 expression. In B-ALLs, 18 of 37 (49%) cases showed OCT-2/BOB.1 co-expression. Individually, 18 of 37 (49%) cases showed OCT-2 expression and 34 of 37 (92%) cases showed BOB.1 expression. In T-ALLs, 4 of 9 cases showed OCT-2/BOB.1 co-expression with all 9 (100%) cases showing BOB.1 expression. 1 of 2 (50%) cases of ambiguous lineage leukemia showed OCT-2/BOB.1 co-expression.
Conclusions: 69% of AML, 49% of B-ALL and 44% of T-ALL show OCT-2/BOB.1 co-expression, with AML showing OCT-2/BOB.1 co-expression most frequently. OCT-2 and BOB.1 are not specific for an immature B-cell lineage as frequent expression was shown by immunohistochemistry in all examined groups of leukemias. This study concludes that these stains would not be a useful tool for lineage designation of acute leukemias.
Category: Hematopathology

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 244, Wednesday Morning


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