Tissue Microarray Is a Useful Tool in the Evaluation of Genes Implicated in Transformation of Follicular Lymphoma.

A subset of patients (pts.) with follicular lymphoma (FL) will transform to a more aggressive histological sub-type, most typically diffuse large B-cell lymphoma (DLBCL). In general response to therapy is poor and survival short. Paired analysis of samples pre- and post transformation suggest that the molecular mechanisms underlying transformation (Tx) are heterogeneous. In order to independently validate recurring changes in gene/protein expression at transformation (GC phenotype of TxDLBCL, Davies et al., 2002; loss of follicular dendritic Cell (FDC) markers, Shiozawa et al., 2003) a Tx-tissue microarray (Tx-TMA) was created comprising serial samples from 35 pts. (median age 54yrs (22–81) at the time of transformation). In these pts. transformation occurred a median of 3.1years from diagnosis (range 0–15.4) and for each pt. ‘set’ at least 1 pre-Tx FL sample (1–3; n=56), and 1 (1–4; n=44) post transformation sample were represented on the array. To ensure that the Tx-TMA cores accurately represented the corresponding full tissue sections a panel of routine immunohistochemical (IHC) diagnostic markers (n=9) were scored. The concordance between Tx-TMA and full sections (n=10) was >90%. The Tx-TMA was then used to investigate the phenotype of transformed DLBCL, according to the germinal centre (GC)/non-GC like model of de novo DLBCL. Using CD10, BCL6 and MUM1 expression to discriminate between the two subclasses of DLBCL the methodology was first validated on a de novo DLBCL TMA (n=31; 20/31 (65%) non-GC, 11/31 (35%) GC phenotype; 5-yr survival for non-GC pts. 51% and for GC pts., 73%). IHC confirmed the results of gene expression profiling indicating that in 31/35 (89%) pts. transformed DLBCL was of GC phenotype (28/35 (80%) CD10+ and 3/35 (9%) CD10-, BCL6+, MUM1-). Of the remainder, 4/35 were CD10-, BCL6+, of which 3/4 were MUM1+ (3/35 (9%) non-GC phenotype; 1/4 MUM1 was not assessable). Similarly the Tx-TMA confirmed loss of FDC markers (CD21 and CD23) on transformation. Samples from 28 pts were evaluable for CD21 and CD23 IHC expression. In 71% (20/28) of pts. the FDC meshwork was lost or became more sparse on transformation (CD21 loss 15/28 (54%); CD23 loss 17/28 (61%)). The most discriminating changes in gene expression on transformation are now being assessed by IHC. Aurora kinase B (ARKB) is an attractive therapeutic target given that disruption of ARK function results in the induction of apoptosis in RL, a t(14:18) positive DLBCL cell line (Harrington et al. 2004). The observed elevation in ARKB transcription on transformation was confirmed by IHC in this series. The Tx-TMA showed ARKB expression increased on Tx in 13/33 (40%) pts., potentially defining a subset of pts. who might be considered for ARKB directed therapies. Expression of ARKB was low throughout in 18/33 (55%) pts and decreased in 2/33 (6%) pts.; difference in ARKB expression was not significantly associated with survival. These preliminary studies suggest that the availability of TMA of serial biopsies from pts. with transformed FL will provide a powerful means of assessing the relevance of gene expression, both within the tumour and the microenvironment while facilitating the selection of patients most likely to benefit from directed therapeutic approaches.