sTRBC1 and cyTRBC1 Expression Distinguishes Indolent T-Lymphoblastic Proliferations From T-Lymphoblastic Leukemia/Lymphoma.

Indolent T-lymphoblastic proliferation (iT-LBP) consists of a proliferation of non-neoplastic TdT + T cells in extrathymic tissues, requiring no treatment. However, due to overlapping clinical and histologic features, distinguishing iT-LBP from T-cell acute lymphoblastic leukemia/lymphoblastic lymphoma (T-ALL/LBL) can be challenging. Recently, flow cytometry-based evaluation of TRBC1 has been used to detect of T-cell clonality in TCRαβ + mature T-cell lymphomas and aid in the differential diagnosis between T-ALL and normal thymocytes. We present a case of iT-LBP with high-grade serous ovarian carcinoma (HGSOC). To investigate the potential utility of TRBC1 expression in distinguishing iT-LBP from T-ALL/LBL, we assessed both surface (s) and cytoplasmic (cy) TRBC1 expression patterns on blast cells from the patient with iT-LBP and HGSOC as well as 11 patients diagnosed with T-ALL/LBL. The results revealed that sTRBC1 and cyTRBC1 exhibited polytypic expression patterns in patient with iT-LBP and HGSOC, while cyTRBC1 showed monotypic expression in those with T-ALL/LBL. This suggests that evaluation of sTRBC1 and cyTRBC1 expression can serve as a simple, rapid, and effective approach to differentiate between iT-LBP and T-ALL/LBL.