Follicular lymphoma with marginal zone differentiation: Microdissection demonstrates the t(14;18) in both the follicular and marginal zone components

On occasion, follicle center lymphomas (FCL) may contain a marginal-zone (M Z) component in which the interfollicular lymphoid cells take on an MZ cell morphology. In the past, these have been termed composite lymphomas. Howev er, recent studies suggest that the two components are clonally related. It is unknown whether the bcl-2 translocation present in most FCLs is present in the cells that demonstrate MZ cell morphology, We have identified three cases of low-grade FCL with a MZ component suitable for laser capture micr odissection (LCM) of the two components. Cases were immunophenotyped in par affin section with antibodies to CD10, CD20, bcl-2, and bcl-6. LCM was done to isolate cells from each component. Polymerase chain reaction for t(14;1 8) using primers to the major breakpoint region was performed on DNA extrac ts. The sensitivity of the PCR assay was decreased to 5%-10% follicle cente r cells in a background of reactive tonsil cells. All three cases showed di fferent phenotypes in each component. The FCL component was positive for al l four of the above markers, whereas the MZ component expressed only CD20 a nd bcl-2. Both components showed t(14;18) amplicons of identical size, with the MZ component signal being stronger than the 5%-10% sensitivity control , suggesting that the signal was not from rare, contaminating FCL cells. Th ese results confirm that both components are clonally related and support t he theory that these are indeed FCLs with MZ differentiation (that retain t he t(14;18)) rather than the reverse, MZ lymphoma with follicle center diff erentiation.