T-lymphoblastic leukemia/lymphoma with interfollicular growth pattern and Castleman-like morphologic features

Indolent T-lymphoblastic proliferation (iT-LBP) is a recently recognized benign pathologic condition commonly associated with Castleman disease. The lymph node of this shows preserved lymphoid architecture nonclonal T-lymphoblasts in the interfollicular area. iT-LBP rare and diagnosis exclusion. As rule, it requires sophisticated techniques to exclude leukemia/lymphoma (T-LBL/L). We present an unusual T-LBL/L mimicking iT-LBP. case showed nodal architecture, morphologic features hyaline vascular disease, area, no clonal T-cell receptor gene rearrangement. follow-up specimen excised 6 months later full-blown lymphoblastic lymphoma abnormal karyotype, near-early-T-precursor phenotype, partial CD19 expression, SETD2 mutation.