Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin's lymphoma (NHL), accounting for 30% to 40% of newly diagnosed cases in the United States.
1 DLBCLs are morphologically and clinically heterogeneous. On the basis of routine pathologic evaluation alone, it is often difficult to reproducibly segregate DLBCLs into clinically distinct groups. Clinical parameters, such as the International Prognostic Index, have been used to predict prognosis.
2 Presumably, the International Prognostic Index reflects underlying differences in tumor biology and genetics.
Gene expression profiling has been used to stratify DLBCLs into prognostically distinct subgroups. One such schema subdivided DLBCLs into germinal center B-cell–like (GCB) DLBCLs, activated B-cell–like (ABC) DLBCLs, and heterogeneous “type 3” subtypes,
3,4 which are associated with distinct genetic alterations.
5 GCB-DLBCL has significantly better survival than the ABC or type 3 groups. A second model developed different expression signatures when cases were grouped according to clinical outcome, defining three subsets: oxidative phosphorylation, B-cell receptor/proliferation, and host response.
6,7 Despite these gene expression advances, the expensive and technically challenging technology is not widely available as a routine laboratory procedure. Consequently, immunohistochemical markers that can place DLBCL into prognostically relevant categories have been identified, sometimes based on the data gleaned from the gene expression profiling research. Using tissue microarrays, CD10, BCL-6, and MUM1 have been validated as such surrogate markers to define DLBCL subtypes by their cell of origin.
8 In one classification scheme, DLBCL is divided into the germinal center (GC) and non-GC groups, which have an overall survival similar to that of the GCB and ABC/type 3 groups identified by expression profiling, respectively.
8 More recently, similar immunohistochemical algorithms have been proposed that also predict clinical behavior.
9,10 Most studies reporting a better outcome of GC DLBCL have been done in patients treated with conventionally dosed chemotherapy alone (usually cyclophosphamide, doxorubicin, vincristine, and prednisone [CHOP]). A better outcome was also found for GC DLBCL in poor-risk patients treated with high-dose sequential therapy and autologous stem-cell transplantation as first-line therapy.
11In patients treated with rituximab (Rituxan, Genentech, South San Francisco, CA), the clinical significance of these DLBCL subclassifications is less clear and controversial. One study showed that the prognostic difference in outcome between patients with GC or non-GC phenotypes no longer exists in patients with de novo DLBCL treated with combination CHOP and rituximab.
12 In contrast, another study found that in patients treated with dose-adjusted etoposide, doxorubicin, vincristine, prednisone, and cyclophosphamide (EPOCH) and rituximab, the GC subtype of DLBCL was associated with a better progression-free survival.
13 Overall, these studies indicate that the prognostic significance of biologic markers is treatment specific.
Other specific proteins evaluated by immunohistochemistry have been shown to have equivocal prognostic validity. High proliferation rate, as determined by Ki-67 (MIB1) expression, has been found to be a strong independent predictor of poor clinical outcome in patients with DLBCL.
14–16 However, other studies have reported that a low proliferative activity is associated with a shorter survival and resistance to chemotherapy in NHL.
17,18 Expression of the antiapoptotic molecule BCL-2 has also been associated with a poor clinical outcome,
16,19,20 although treatment with rituximab seems to eliminate the poor risk conferred by BCL-2 expression.
13,21 One previous study reported that high BCL-2 expression or proliferation index does not impart a poor outcome in patients with AIDS-related DLBCL treated with dose-adjusted EPOCH.
22 High-level expression of FOXP1, a transcription factor differentially expressed in resting and activated B cells, is correlated with the non-GC phenotype and has been reported to be an independent adverse prognostic marker for DLBCL.
23–25 Recently, smaller FOXP1 isoforms were found in some DLBCLs; these shorter forms are induced by B-cell activation and are potentially oncogenic.
26 Another protein that has received significant attention for its role in plasma cell differentiation is B-lymphocyte-induced maturation protein (Blimp-1)/PRDM1 (reviewed in
27,28). Some DLBCLs express Blimp-1 and display more aggressive behavior, with a shorter failure-free survival.
29NHL is the second most common malignancy in HIV-infected individuals and is an AIDS-defining condition. The relative risk of NHL in people with AIDS has been estimated to be more than 100-fold higher than that of the general population.
30 DLBCL is the most common form of HIV-associated NHL. Although extensive investigative work has been conducted on DLBCL in immunocompetent patients as reviewed above, little is known about the impact of subclassification of DLBCL in the setting of AIDS. The immunophenotypic profile and subclassification of AIDS-related DLBCL into B-cell differentiation categories has been reported in two studies that did not include clinical information.
31,32 A study that included clinical data found that the non-GC phenotype was associated with a worse outcome in 89 nonuniformly treated HIV-positive patients with DLBCL.
33 Only one previous study reported immunohistochemical characterization and correlation with clinical data in a panel of 25 HIV-positive patients with DLBCL who were uniformly treated with dose-adjusted EPOCH.
22 To expand on that study and further evaluate whether immunophenotypic subclassification could help prognosticate cases of AIDS-related DLBCL in a larger cohort of patients, we examined cases of DLBCL from the AIDS Malignancy Consortium (AMC) clinical trials 010 (CHOP
v CHOP-rituximab) and AMC034 (EPOCH-rituximab concurrent
v sequential). We investigated whether a GC versus non-GC immunophenotype; the presence or absence of FOXP1, Blimp-1, or BCL-2 protein expression; Epstein-Barr virus (EBV) infection; or the proliferation index was correlated with overall or disease-free survival in AIDS patients with DLBCL.