Brar N, et al. Histopathology 2020.
AIMS: An indolent T-lymphoblastic proliferation (iT-LBP) is a benign, reactive expansion of immature TdT+ T-cells found in extrathymic tissues. iT-LBP can be challenging to distinguish from malignant processes, specifically T-lymphoblastic lymphoma (T-LBL), given the overlapping clinical and histologic features. Recently, it has been shown that LIM domain only 2 (LMO2) is overexpressed in T-LBL but not in reactive immature TdT+ T-cells in the thymus. Based on these findings, we investigated the expression of LMO2 by immunohistochemistry and its role in differentiating iT-LBPs from T-LBLs.
METHODS: We retrospectively identified cases of iT-LBP and T-LBL from the pathology archives of four institutions. Seven cases of iT-LBP (including five new cases that have not been reported in the literature) and 13 cases of T-LBL were analyzed. Clinical, morphologic, immunophenotypic and molecular data were analyzed. Immunohistochemical staining with LMO2 was performed on all cases of iT-LBP and T-LBL.
RESULTS: A review of five new cases of iT-LBP showed similar morphologic, immunophenotypic and molecular features to prior reported cases. All cases of iT-LBP were negative for LMO2 (0/7) while 92% of T-LBL cases (12/13) expressed LMO2; sensitivity 92% (confidence interval 64-100%) and specificity 100% (confidence interval 59-100%).
CONCLUSION: We confirm prior published findings that cases of iT-LBPs demonstrate highly overlapping morphologic and immunophenotypic features when compared to T-LBL. Importantly, expression of LMO2 is a sensitive and specific marker to rule out iT-LBP.