Diffuse large B-cell lymphoma (DLBCL) is a common subtype of primary gastric lymphoma,
accounting for 50–60% of cases.
1
Prior to the rituximab era, a Japanese phase II trial evaluated three courses of cyclophosphamide,
doxorubicin, vincristine and prednisolone (CHOP), followed by 40.5 Gy of involved
field radiotherapy (IFRT) for localized (stage I, II1 based on the Lugano Staging
System for Gastrointestinal Lymphoma
2
) primary gastric DLBCL (PG-DLBCL) and the study yielded good therapeutic results.
3
Rituximab plus CHOP (R-CHOP) therapy has been shown to improve the prognosis of DLBCL
patients over that of patients treated with CHOP.
4, 5
The efficacy of three cycles of R-CHOP followed by IFRT for localized DLBCL was evaluated
in a phase II trial by the Southwest Oncology Group and also showed favorable results.
6
On the basis of these findings, a rituximab-containing regimen, particularly three
cycles of R-CHOP followed by IFRT, is regarded as one of the standard therapies for
localized DLBCL including PG-DLBCL. Recent studies demonstrated that the double rearrangement
(double hit) of the MYC and BCL2 genes and the double expression of the MYC and BCL2
proteins were associated with a poor prognosis for patients with nodal DLBCL.
7, 8, 9, 10
However, the clinical impact of the double expression of MYC and BCL2 on PG-DLBCL
remains unknown. We retrospectively analyzed patients with localized PG-DLBCL who
were initially treated with a rituximab-containing regimen, with a focus on the status
of MYC and BCL2.
We retrospectively analyzed 52 consecutive patients newly diagnosed with localized
PG-DLBCL at our institution between 2003 and 2013. They were initially treated or
planned to be treated with a rituximab-containing regimen. All patients underwent
standard staging procedures, including upper gastrointestinal endoscopy, bone marrow
aspiration or biopsy, computed tomography, and/or fluorine-18-2-fluoro-2-deoxy-D-glucose
positron emission tomography/computed tomography and were assigned a clinical stage
according to Lugano Staging System for Gastrointestinal Lymphomas.
2
This retrospective study was approved by the Institutional Review Board of the National
Cancer Center in Japan. It was conducted in accordance with the international ethical
recommendations stated in the Declaration of Helsinki and Japanese Good Clinical Practice
Guidelines. Histopathological diagnoses were made and reviewed by two experienced
hematopathologists (AMM and HT) according to the criteria of the WHO classification.
11
An immunohistochemical analysis of formalin-fixed, paraffin-embedded tissues was performed
using a panel of monoclonal antibodies. MYC immunoreactivity was considered positive
when the MYC protein was expressed in more than 40% of tumor cells. BCL2 was considered
positive when the BCL2 protein was expressed in more than 70% of the tumor cells.
7
Lymphoma cells were assigned a germinal center B-cell-like (GCB) or non-GCB phenotype
using the Hans algorithm for cell-of-origin subtyping.
12
A fluorescence in situ hybridization analysis was performed on formalin-fixed, paraffin-embedded
tissue sections. The following probes were used: an LSI MYC dual-color break apart
rearrangement probe and LSI IGH/BCL2 dual-color dual-fusion translocation probe (Vysis,
Downers Grove, IL, USA). Overall survival (OS) was defined as the interval between
the date of diagnosis and date of death or last follow-up. Progression-free survival
was defined as the interval between the date of diagnosis and date of death, disease
progression or last follow-up. Survival analyses were performed using Kaplan–Meier's
method and compared using the log-rank test. All P-values were based on two-sided
tests and P-values <0.05 were considered significant. Statistical analyses were performed
using EZR version 1.27.
13
The characteristics of all 52 patients are shown in Table 1. Twenty-four patients
(46%) were male and 28 (54%) were female with a median age of 62 years (range: 29–85).
Performance statuses were 0–1 in 47 patients (90%). Thirty patients (58%) presented
with stage I disease, 15 (29%) with stage II1, 2 (4%) with stage II2 and 5 (9%) with
stage IIE. Most patients (47 patients: 90%) had a low or low-intermediate risk according
to the International Prognostic Index.
14
Serum lactate dehydrogenase levels were normal in 45 patients (87%). Forty-eight patients
(92%) lacked B symptoms.
The details of treatments were as follows: 43 patients (83%) received R-CHOP followed
by IFRT, 7 (13%) received R-CHOP alone, 1 (2%) underwent total gastrectomy followed
by rituximab because the patient denied chemotherapy and IFRT, and 1 (2%) received
CHOP plus IFRT. The median number of CHOP cycles was three (range: 2–8). Most patients
(43 patients: 83%) were treated with R-CHOP plus IFRT. The median dose of IFRT was
40 Gy (range: 30–40 Gy).
The Ki-67 index was ⩾90% in 25 out of 46 evaluable patients (54%). The cell-of-origin
subtype was assigned in 48 of the 52 patients (30 patients (63%) GCB and 18 patients
(37%) non-GCB). The double expression of MYC and BCL2 was assessed in 47 out of 52
patients (90%), and confirmed in 7 (15%). MYC break apart was detected in 1 out of
24 patients (4%) evaluated by fluorescence in situ hybridization. IGH/BCL2 fusion
was confirmed in 1 out of 27 evaluable patients (4%). MYC break apart and IGH/BCL2
fusion were both assessed in 22 patients including 5 with the double expression of
MYC and BCL2. However, no patient had the double hit of MYC break apart and IGH/BCL2
fusion.
The median follow-up duration was 76 months (range: 4–127 months). Fifty patients
(96%) achieved complete response, and the remaining two patients without the double
expression of MYC and BCL2 had primary refractory disease. The estimated 5-year OS
and progression-free survival rates of all 52 patients were 90% (95% confidence interval
(CI), 75–96%) and 89% (95% CI, 75–95%), respectively (Figure 1a). The estimated 5-year
OS rates of patients with and without the double expression of MYC and BCL2 were 100%
and 87% (95% CI, 69–95%), respectively (Figure 1b). No significant difference was
observed between the two cohorts (P=0.74). The estimated 5-year OS rates of the GCB
phenotype and non-GCB phenotype were 86% (95% CI, 63–96%) and 93% (95% CI, 59–99%),
respectively, and this difference was not significant (P=0.99). Six out of 52 patients
died. The causes of death were as follows; two were due to the progression of DLBCL
without the double expression of MYC and BCL2, and the remaining four died of other
cancers without DLBCL.
The results of the present study revealed the good prognosis of patients with localized
PG-DLBCL treated with rituximab-containing chemotherapy with or without IFRT, and
demonstrated that double expression of MYC and BCL2 did not influence patient outcomes.
Although CHOP followed by IFRT is regarded as one of the standard therapies for localized
PG-DLBCL, information in the rituximab era has been limited. Our study confirmed the
efficacy and feasibility of R-CHOP plus IFRT, and this strategy is considered to be
a reasonable standard therapy for localized PG-DLBCL in the rituximab era.
The prognosis of nodal DLBCL patients with the double expression of MYC and BCL2 treated
with R-CHOP therapy was significantly worse in previous studies,
7, 8, 9, 10
and it was also shown that the prognosis of patients with the double expression and
double hit was not significantly different.
7
There is currently no standard therapy for DLBCL patients with the double hit or double
expression. Several studies have suggested that more intensive chemotherapies than
R-CHOP or stem cell transplantation may overcome the poor prognosis of double hit
lymphoma.
15
However, these hypotheses have mainly been discussed for nodal DLBCL. The results
of the present study suggest that R-CHOP followed by IFRT is sufficient for most localized
PG-DLBCL patients with the double expression of MYC and BCL2. On the other hand, as
no double hit patients were included, it was not possible to evaluate the impact of
the translocation in our study.
There were several limitations to this study. This was a retrospective analysis conducted
at a single institution. The number of patients and events was too small to draw any
definitive conclusions. Although most patients received R-CHOP plus IFRT, 17% were
treated with other regimens. Specimen availability differed in each patient; therefore,
the profiles of all patients were not assessed for the double hit or double expression
of MYC and BCL2.
In conclusion, the results of the present study showed good prognoses, and suggest
that the double expression of MYC and BCL2 did not influence the outcomes of localized
PG-DLBCL patients treated with rituximab-containing chemotherapy with or without RT.
Further investigations are needed in order to confirm our results.