Bone marrow involvement by peripheral t-cell lymphoma, not otherwise specified

Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), is a subgroup of mature T-cell lymphoma that does not fit into any well-defined subtype of T-cell lymphomas. It is mainly present in lymph nodes, but any extranodal sites may be involved, with approximately 30% of cases showing bone marrow involvement. Occasionally, the initial diagnosis of PTCL-NOS is made on a bone marrow biopsy. Although PTCL-NOS, as a group, is morphologically heterogeneous, in each individual patient, it often shows similar morphologic features in the involved bone marrow and extramedullary sites. It often demonstrates an abnormal immunophenotype, with frequent loss or decrease in the expression of pan T-cell antigens, most commonly CD5 or CD7. Here, we report 2 cases of PTCL-NOS to demonstrate the morphologic heterogeneity and the importance of immunophenotyping using both immunohistochemistry and flow cytometry analysis for the evaluation of bone marrow involvement.