Clonally related follicular lymphomas and histiocytic/dendritic cell sarcomas: evidence for transdifferentiation of the follicular lymphoma clone.

Laboratory of Pathology, National Cancer Institute, Bethesda, MD, United States.

Rare cases of histiocytic and dendritic cell neoplasms (H/DC) have been reported in patients with follicular lymphoma (FL), but the biologic relationship between the two neoplasms is unknown. We studied eight patients with both FL and (H/DC) neoplasms using immunohistochemistry, fluorescence in situ hybridization (FISH) for t(14;18), and PCR/sequencing of Bcl2 and IgH rearrangements. There were 5 men and 3 women (median age, 59y). All cases of FL were positive for t(14;18). The H/DC tumors included 7 histiocytic sarcomas, 5 of which showed evidence of dendritic differentiation and 1 interdigitating cell sarcoma. Five H/DC tumors were metachronous, following FL by 2 mos to 12 yrs; tumors were synchronous in 3. All 8 H/DC tumors showed presence of the t(14;18) either by FISH, or in two cases by PCR with the major breakpoint region (MBR) probe. PCR and sequencing identified identical IgH gene rearrangements or BCL2 gene breakpoints in all patients tested. All H/DC tumors lacked PAX5 and upregulation of CEBPbeta and PU.1 was seen in all cases tested. These results provide evidence for a common clonal origin of FL and H/DC neoplasms when occurring in the same patient, and suggest that lineage plasticity may occur in mature lymphoid neoplasms.

PMID: 18272816 [PubMed - as supplied by publisher]