[1442] NOTCH1 Intracellular Domain Immunohistochemistry as a Diagnostic Tool To Distinguish T-Lymphoblastic Lymphoma from Thymoma

Armin G Jegalian, Juraj Bodo, Timothy R Holzer, Janet M Grondin, Angie D Fulford, Bradley L Ackermann, Robert J Konrad, Aejaz Nasir, Andrew E Schade, Eric D Hsi. Cleveland Clinic, Cleveland, OH; Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN

Background: Differentiating T-lymphoblastic leukemia/lymphoma (T-LBLL) and thymoma can be problematic due to a predominance of precursor T-cells in both. Because of very different clinical implications, accurate diagnosis is critical. T-LBLLs are characterized by frequent activation of the NOTCH1 signaling pathway, which plays a central role in the pathogenesis of this disease. With the development of antibodies to NOTCH1 Intracellular Domain (N1ICD), which recognize the active form of NOTCH1, we hypothesized that detection of N1ICD would be useful in distinguishing T-LBLL from thymoma.
Design: We investigated a series of formalin fixed paraffin embedded tissues (FFPET) from T-LBLL, B-lymphoblastic lymphomas (B-LBLL), and thymomas for immunoreactivity with a N1ICD (Val1744) antibody using automated immunohistochemistry. Slides were scored using a 25% nuclear reactivity threshold for positivity.
Results: Specificity of the antibody staining was confirmed with Western blot and immunostaining of FFPET cell blocks of a rat kidney epithelial cell line (RK3E) stably transfected with a γ-secretase-dependent, truncated murine Notch1. Hyperplastic tonsil showed positivity in only few scattered interfollicular lymphocytes and immunoblasts, few epithelial cells, and endothelial cells. Normal bone marrow demonstrated immunoreactivity in maturing granulocytic elements. Thymocytes from non-neoplastic thymus were largely negative for N1ICD as were B-LBLL cells (n=3). All 16 T-LBLL cases were scored positive for N1ICD. Eight (50%) of the T-LBLL cases showed strong and diffuse immunoreactivity, whereas the remaining 8 (50%) were more variable, but with consistently greater than 25% nuclear staining. Whether this variation reflects differences in NOTCH1 pathway mutations is not yet known. All 21 thymomas were negative for N1ICD although epithelial cells and a small minority of thymocytes may be positive, requiring careful interpretation.
Conclusions: Normal thymocytes do not express appreciable levels of N1ICD. In keeping with this pattern, thymomas are negative for N1ICD while a high percentage of T-LBLL expresses N1ICD. Thus, immunohistochemistry for N1ICD appears to be a useful maker in distinguishing T-LBLL from thymoma.
Category: Hematopathology

Tuesday, March 20, 2012 8:30 AM

Platform Session: Section C, Tuesday Morning


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