What Is Anaplastic Large Cell Lymphoma?

CD4-positive diffuse large B cell lymphoma identified by flow cytometry: two case reports

We report two cases of diffuse large B cell lymphoma (DLBCL), both occurring in the small bowel, which coexpress PAX5, weak or no CD20 and the CD4 antigen. The CD4 was initially identified by flow cytometry and then confirmed by immunohistochemistry. CD4 is a representative marker for helper T-lymphocytes and is present on a subset of thymocytes, peripheral T cells and monocytes or macrophages. Unlike CD2 and CD5, no B cell fractions are known to express CD4. It might be hypothesized that the deregulated control of gene expression in malignant B cells, in particular PAX5, leads to the activation of some silent or repressed genes of T cell differentiation. Although lineage infidelity is described in some B lymphomas, it remains as an uncommon phenomenon; to our knowledge, cases reported here are the first two cases of DLBCL of the gastrointestinal tract coexpressing the CD4 antigen to be described to date.

CD3-positive large B-cell lymphoma

It is not uncommon for some B-lineage non-Hodgkin lymphomas (NHLs) to aberrantly coexpress T-cell markers, particularly CD5, as well as CD7, CD2, CD4, and/or CD8 in rare cases. Cases of CD3-positive B-cell NHL, however, have not previously been described in the literature. We present 4 cases of large B-cell lymphoma aberrantly coexpressing T-cell marker CD3 and B-lineage markers as well as demonstrating clonal rearrangement of the immunoglobulin genes but not the gamma T-cell receptor gene. To our knowledge, this represents the first series report of B-cell NHL coexpressing T-lineage-specific marker CD3. The identification of such cases indicates that the use of CD3 antibody alone in paraffin sections may lead to an incorrect determination of cell lineage in some B-cell NHL. Immunohistochemistry using additional cell lineage specific markers or molecular analysis for antigen receptor gene rearrangements are necessary for correct determination of the cell lineage in such cases.