Characterisation of molecular alterations in diffuse large b-cell lymphoma with respect to transformation, progression and prognostic markers

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma type, and
comprises nearly 500 newly diagnosed cases in Sweden every year. DLBCL is a group of
aggressive lymphomas that are extremely heterogeneous and differ in morphology,
immunophenotype, molecular and clinical features as well as in response to therapy. 



The transformation of low malignant lymphoma, most commonly follicular lymphoma (FL), to
DLBCL is associated with a progressive disease and poor prognosis. The overall aim of this
thesis was to identify the genetic events underlying the progression and transformation of
indolent FL to aggressive DLBCL and to outline molecular alterations distinguishing DLBCL
with germinal center (GC) and non-GC phenotype. 



In search for novel markers in lymphoma, we have investigated an anti-apoptotic protein,
HS-associated protein X-1 (HAX-1), at the protein and transcript level in malignant
lymphomas (paper I). We found high levels of HAX-1 mRNA and protein expression in Bcell
lymphomas. We also identified a positive association between proliferation (Ki67) and
HAX-1 expression, as well as an inverse correlation between Bcl-2 and HAX-1 demonstrated
on a transcript and protein level in FL, which indicates the potential role of HAX-1 as a Bcl-2
homolog. 



In papers II and III we studied paired tumours of FL and its transformed DLBCL
(tDLBCL) counterparts and compared with de novo DLBCL (dnDLBCL) using arraycomparative
genome hybridisation (array-CGH) in order to outline genetic alteration of
importance for the transformation process. We identified a gain of 2p15-16.1 as a potential
prognostic marker, and that this alteration may appear already in the FL prior to
transformation. This chromosomal region encompasses, among others, genes involved in NF-
κB pathway, such as REL, USP34, COMMD1, OTX1 and of known importance for B-cell
development, such as BCL11A. We have also performed whole exome sequencing (WES)
results in a smaller group of patients with consecutive lymphoma samples. A comparison
with array-CGH data showed that these two methods complement and strengthen each other
in pinpointing crucial genetic events. Furthermore, our studies revealed that clonal evolution
of transformed tumours occurs according to the branching model. A number of mutations
identified in the peri-transformation phases – defined as FL appearing prior and tDLBCL
directly after transformation - affected genes involved in histone modifications, cell cycle,
apoptosis, PI-3 kinase pathway, and Ras signalling pathway. 



In Paper IV we performed proteomic profiling of DLBCL subtypes i.e. non-GC and GC, and identified 91 proteins
present exclusively in the non-GC type of DLBCL. We focused on two proteins of
importance for the NF-κB pathway (BiP and Hsp90) as well as on Cyclin B2. We observed
increased expression of these three proteins in DLBCL and also in non-GC vs GC type of
DLBCL. These findings suggest a potential relevance of these proteins as prognostic markers
and may lead to new treatment options