Haematologica, Vol 92, Issue 1, e1-e2 doi:10.3324/haematol.10255
Copyright © 2007 by Ferrata Storti Foundation
Re-occurrence of the CD20 molecule expression subsequent to CD20-negative relapse in diffuse large B-cell lymphoma
A.J. Ferreri1,,
G.P. Dognini1,
C. Verona1,
C. Patriarca2,
C. Doglioni3,
M. Ponzoni3
1 Medical Oncology; San Raffaele H Scientific Institute, Milan, Italy
3 Pathology Units; Dept. of Oncology; San Raffaele H Scientific Institute, Milan, Italy
2 Division of Pathology; Ospedale di Melegnano, Melegnano, Italy
Correspondence: Andrés J. M. Ferreri, MD, Medical Oncology Unit Dept. of Oncology, San Raffaele H Scientific Institute, Via Olgettina 60, 20132 - Milan, Italy, Tel: 0039-02-26437649 Fax: 0039-02-26437625, e-mail: andres.ferreri{at}hsr.it

ABSTRACT
We report the first case of diffuse large B-cell lymphoma (DLBCL)
of the stomach displaying CD20-negative relapse after rituximab-containing
treatment and the re-appearance of CD20 expression at the second
failure. The loss of CD20 expression in B-cell lymphomas relapsing
after rituximab is a well-known phenomenon, but its actual impact
in DLBCL is difficult to estimate. This paradigmatic case suggests
that CD20-expression reappearance after purging of CD20-positive
clones with rituximab might be an underestimated occurrence
in B-cell lymphomas. Accordingly, every relapse, whenever possible,
should be histologically assessed with diagnostic and immunophenotyping
purposes.

Case report
A 85-year-old male with a history of hepatitis C virus infection
was admitted at Our Institution with a diagnosis of diffuse
large B-cell lymphoma (DLBCL) of the stomach (Ann Arbor stage
IEA). Immunophenotypic analysis on diagnostic samples obtained
by multiple gastroscopic biopsies showed CD20 expression (L26
clone) in 100% of neoplastic cells (
Figure 1a). The patient
was treated with a conservative strategy consisting of four
courses of chemo-immunotherapy with rituximab 375 mg/m
2 on day
1, cyclophosphamide 600 mg/m
2 on day 1, epidoxorubicin 50 mg/m
2 on day 1, vincristine 2 mg on day 1, prednisone 50 mg daily
on days 1 to 5, every 28 days. A pathologically documented complete
response was obtained since the second course. At six months
from therapy conclusion, a local relapse, consisting of a 5-cm
ulcer in the posterior wall of the stomach, was found. The evaluation
of nine gastric biopsies showed a diffuse proliferation of CD20
(L26)-negative/CD79a-positive (
Figure 1b) large cells. CD20-negative
phenotype was confirmed with an additional anti-CD20 monoclonal
antibody reactive against the C-terminal intracellular domain
of the transmembrane CD20 molecule (7D1 clone, Novocastra, Newcastle,
UK). The second-line therapy was 39.6 Gy irradiation to the
stomach and regional lymph nodes, thus obtaining a second pathological
complete remission. At six months from the last relapse, a further
local recurrence consisting of a large gastric ulcer was diagnosed.
Histological evaluation of multiple biopsies showed a picture
of DLBCL with the expression of CD20 molecule in 10% of neoplastic
cells; CD20 immunoreactivity was detected by using both L26
and 7D1 monoclonal antibodies (
Figure 1c). It was not possible
to start a new treatment since the patients general conditions
gradually worsened; he died of progressive lymphoma at 16 months
from original diagnosis.

Discussion
This case displays two unreported features. To the best of our
knowledge, this is the first case of gastric DLBCL displaying
CD20-negative relapse after rituximab treatment. The loss of
CD20 expression in non-Hodgkin lymphomas (NHL) relapsing after
rituximab is a well-known phenomenon. This occurrence has been
interpreted as a mechanism of drug resistance to this drug and,
likely, due to the selection of pre-existing CD20-negative neoplastic
cells or to the induction of mutated CD20-negative clones
1.
The actual impact of this phenomenon is difficult to estimate
2–4 since the reported prevalence oscillates between 0%
3 and 46%
5 of relapses; they are mostly described in follicular lymphomas,
1,5 rarely in DLBCL
6. These discordant prevalence figures may be
due to the different assays employed for the detection of CD20
molecule. Rituximab itself, by virtue of its blocking CD20-binding
sites, which lasts up to 6 months, can result in an apparent
CD20 negativity at flow cytometry
3. Accordingly, the immunostain
with L26 antibody, which recognizes the CD20 intracellular domain,
should be performed to define CD20 negativity
7, while CD79a,
another B-cell marker, may be a useful tool in the identification
of lymphomatous CD20-negative (L26-negative) B-cells in some
particular settings.
2,8 Our patient experienced a real CD20-negative
relapse, considering that tumor cells displayed an L26-negative/7D1-negative/CD79a-positive
pattern. These histopathological features are reliable, since
they were carried out on several biopsies, and the immunophenotype
of tumor cells and internal positive controls (small B-lymphocytes;
Figure 1b) was constant among different bioptic samples.
The second and most intriguing aspect of our case is the re-appearance of CD20 expression at the second failure, following a previous CD20-negative relapse. No other cases with similar characteristics have been reported in literature; this depends on the fact that patients with multiple relapses of nodal or extranodal NHL are rarely referred to systematic surgical biopsy, while this latter strategy is a current practice during the follow-up of gastric lymphomas. This paradigmatic case suggests therefore that CD20-expression reappearance after purging of CD20-positive clones with rituximab might be an underestimated occurrence in B-cell lymphomas. Accordingly, every relapse, whenever possible, should be histologically assessed with diagnostic and immunophenotyping purposes. In particular, re-immunophenotyping may have relevant therapeutic implications considering that the loss of CD20 expression prevents to retreat these patients with rituximab or radiolabeled anti-CD20 antibodies as salvage therapy. Conversely, the CD20-expression reappearance, and a progressively further increase in CD20-positive cells amount, could allow the use of anti-CD20 therapy (mostly radiolabeled monoclonal antibody) once again. This is a very important issue since re-treatment with rituximab has been associated with a 42% remission rate and a median progression-free survival of 20 months;9 while the use of 90Y-ibri-tumomab tiuxetan, an anti-CD20 radioimmunoconjugate, resulted in a 74% response rate in rituximab-refractory lymphomas.10 In conclusion, our findings support the strategy to perform biopsy with CD20 immunostaining in any patient with relapsed lymphoma, potentially eligible for anti-CD20 therapy. Since its relevant therapeutic implications, this diagnostic strategy should be strongly recommended in NHL patients.

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