Detection of BCL2 Gene Rearrangements in the Reed-Sternberg Cells of Composite Lymphomas or Newly Diagnosed Hodgkin Lymphoma in Patients with a Previous Diagnosis of Follicular Lymphoma

Introduction:

Composite lymphomas involving Hodgkin lymphoma (HL) and non-Hodgkin lymphomas (CLL, DLBCL, FL, MZL, MCL, T-NHL) are relatively rare but are increasingly frequently diagnosed. This may be a function of the change in diagnostic practice, the more varied and increased treatment of the presenting disease or simply reflect better monitoring post treatment with re-biopsy of lymph nodes. Composite lymphoma is defined as the synchronous and metachronous development of two or more lymphomas in the same patient. The mechanism of pathogenesis underlying its occurrence is not clearly established and in particular the relationship between entities when HL is diagnosed a number of years following successful treatment for follicular lymphoma (FL).

Methods:

We identified 48 patients with a diagnosis of Hodgkin lymphoma at our centre between January 2005 and June 2014 who had a previous or concurrent diagnosis of another lymphoproliferative disorder. Diagnoses included CLL = 14; follicular lymphoma = 13; DLBCL = 8; mantle cell lymphoma = 1; marginal zone lymphoma = 5; T-cell lymphoma = 3; not specified = 3 and a single patient had CLL, MZL and most recently MCL. The diagnosis of Hodgkin lymphoma was confirmed on the tissue biopsy by using a standard panel of immunohistochemistry markers (CD3, CD20, CD30, IRF4, TARC, CD79, LMP1, BCL6, BOB1, OCT2). This study is focussed on the 13 cases with follicular lymphoma. The aim of the study was to identify a relationship between the Hodgkin lymphoma and the follicular lymphoma using interphase FISH studies to look for identical chromosomal translocations.

Results:

8/13 patients had follicular lymphoma diagnosed on an earlier tissue biopsy, range 1-9 years prior to the diagnosis of Hodgkin lymphoma; 7/8 of these FL cases had bone marrow staging carried out at presentation and 5/7 had involvement by FL. 5/13 were newly presenting patients with composite lymphoma; 3/5 had a staging marrow which in each case showed evidence of follicular lymphoma alone with no evidence of Hodgkin lymphoma. In total, 7/13 patients fit the criteria for composite lymphoma with Hodgkin lymphoma and follicular lymphoma occupying distinct zones within the same tissue biopsy. The remaining 6/13 patients show no evidence of follicular lymphoma in the current biopsy and are indistinguishable from de novo presentation of Hodgkin lymphoma. Interphase FISH was used to assess for a genetic relationship between the disease entities. 3µ sections were cut from formalin fixed paraffin processed tissue, using the same block where possible as the H&E and immunohistochemistry. All cases were independently assessed by two experienced scientists with knowledge of histology and FISH reporting on thin sections. 8/13 cases had suitable samples for FISH, the remaining 5 cases had insufficient material remaining in the block. Commercial probes for BCL2 ‘Split-Signal’ (Abbott/Vysis or Dako) were used and FISH results were examined using a Zeiss microscope with MetaSystem image capture. All 8 cases showed BCL2 gene rearrangement in the Reed-Sternberg (RS) cells (5/8 cases were de novo group of Hodgkin lymphoma with no morphological or phenotypic evidence of FL in the tissue and 3/8 were composite lymphoma with distinct zoning). One rare case contained RS cells in a dab/imprint preparation made from the fresh tissue, FICTION technique was carried out on this case combining CD30 immunofluorescent staining with FISH for BCL2 gene rearrangement confirming RS cell type with BCL2 gene rearrangement.

CONCLUSIONS

The identification of BCL2 gene rearrangement in RS cells, the hallmark cell of Hodgkin lymphoma, in this series of composite lymphomas suggests a relationship between the B cells of follicular lymphoma and the RS cells of HL. The presence of the same chromosomal abnormalities identified in more than one lymphoma cell type indicates the same clonal cell of origin.