Leukocyte common antigen (CD45) negative follicular lymphoma, a rare immunophenotypic presentation

CD45 is universally expressed on nucleated hematopoietic cells in healthy individuals with variable intensities. Although down-regulation of CD45 expression is commonly seen in immature B-cell neoplasm, loss of CD45 expression is rarely observed in mature B-cell lymphoproliferative disorders.

A 64-y old man was presented with fatigue and night sweat in July 2013. Physical examination revealed right axillary lymphadenopathy without splenohepatomegaly. The lymph node was sent for flow cytometry and histomorphologic evaluation. Flow cytometric analysis revealed the presence of CD45+ and CD45- cell populations. The CD45+ population (42%) comprised mainly unremarkable CD3+ T cells. However, the CD45- population (35%) showed CD19+, CD20+, and CD10+ immunophenotype with monotypic surface Lambda immunoglobulin light chain expression. Immunohistochemical studies performed on tissue section revealed that neoplastic lymphoid nodules were positive for CD20, BCL-6 and BCL-2 with low proliferation index by Ki-67 staining, but again negative for CD45. FISH analysis confirmed the presence of IGH/BCL2 rearrangement. Follicular lymphoma (grade 1) with negative CD45 expression was diagnosed.

Loss of CD45 expression has been reported, but all cases documented were large B cell lymphoma (LBCL). To the best of our knowledge, this is the first case of low grade follicular lymphoma with lack of CD45 expression. We report this case because of not only its rarity but also to raise awareness that loss of CD45 expression can occur in LBCL as well as in low grade B-cell lymphomas.