Relapse of follicular lymphoma arising from a non-t(14;18) clone

Intraclonal diversity is commonly observed in patients with follicular lymphoma (FL), whereas tumor cells at the onset and relapse usually share early genetic events such as VDJ rearrangement of the immunoglobulin genes and t(14;18) translocation. We report a case of FL with relapse with FL that was clonally different from the tumor cells at onset. A 59-year-old male presented with paraaortic lymph node swelling and thickening of the right renal pelvic and ureteral wall was histologically diagnosed as FL, grade 1. Karyotypic analysis revealed t(14;18)(q32;q21) with +12 and +der(18)t(14;18). Ten years after the initial diagnosis, he suddenly developed systemic lymphadenopathy as a second relapse, and histological examination led to the diagnosis of FL grade 3B with diffuse large B-cell lymphoma. Surprisingly, karyotypic analysis demonstrated the presence of +12 and 3q27 abnormality, which was proved to be a BCL6 translocation by fluorescence in situ hybridization, but the absence of t(14;18)(q32;q21). We compared VDJ rearrangement of the FL cells at onset and relapse and found that they were completely independent of each other. These tumor cells sharetrisomy 12 as a common genetic abnormality, and it is speculated that trisomy 12 may have occurred earlier than BCL2 and BCL6 translocations. These results suggest that there can even be cases of "relapse" of FL with an independent origin of the primary tumor cells. Our observation highlights the importance of re-biopsy of relapsed FL, especially when it occurs after a long remission with different clinical presentation from that at the onset.