CD3- CD56+ non-Hodgkin's lymphomas with an aggressive behavior related to multidrug resistance.

CD56 expression has been reported previously in some non-Hodgkin's lymphoma (NHL) characterization. They principally involve the nasopharynx, are related to Epstein-Barr virus (EBV), and may be classified as either T- or non-T-natural killer (NK) cells according to CD3/T-cell receptor (TCR) status at the genomic or protein level. The present study reports three cases of non-nasal NK-NHL with the following characteristics: an agressive clinical behavior, heterogenous morphological data evoking pleomorphic T-cell malignant lymphoma, a non-T-NK phenotype using flow cytometry, and immunochemistry. The three cases were CD56+ without membrane expression of specific T markers (CD3, CD5, and TCR). Heterogenous results were observed concerning different antigens: CD2, CD4, CD8, CD16, CD94, CD122, TiA1, perforin, and granzyme B. There was no evidence of detectable clonal TCR gene rearrangement with polymerase chain reaction. No NK activity was detected in the two tested cases, and no relation was found with EBV. Multidrug resistance investigations suggest that agressive clinical findings could be related to MDR1 gene expression as confirmed by MDR1 mRNA detection, MDR1 gene product (Pgp) expression, and a functional multidrug resistance study using rhodamine efflux by flow-cytometry.