Mantle cell lymphoma with aberrant expression of CD10

U Zanetto, H Dong,1 Y Huang,2 K Zhang,3 M Narbaitz,4 S Sapia,5 I Kostopoulos,6 H Liu,2

M-Q Du2 & C M Bacon2

Department of Pathology, City Hospital, Birmingham, UK, 1Genzyme Genetics, New York, NY, USA, 2Department of

Pathology, University of Cambridge, Cambridge, UK, 3Geisinger Medical Center, Danville, PA, USA, 4Pathology Service,

Instituto de Investigaciones Hematologicas, Academia Nacional de Medicina, 5Department of Haematopathology, Fundaleu,

Buenos Aires, Argentina, and 6Department of Pathology, Aristotle University of Thessaloniki, Thessaloniki, Greece

Date of submission 13 December 2007Accepted for publication 25 January 2008

Zanetto U, Dong H, Huang Y, Zhang K, Narbaitz M, Sapia S, Kostopoulos I, Liu H, Du M-Q & Bacon CM

(2008) Histopathology 53, 20–29

Mantle cell lymphoma with aberrant expression of CD10

Aims: Morphological, immunophenotypic and geneticheterogeneity amongst mantle cell lymphomas (MCLs)can lead to difficulties in diagnosis and management.The aim was to describe the clinical and patho-logical features of MCLs with aberrant expression ofCD10.Methods and results: Of 17 specimens from 13 patients,14 expressed CD10 and three (presenting before orafter a CD10+ specimen) did not. All expressed cyclinD1 and carried the t(11;14)(q13;q32) ⁄ CCND1-IGHtranslocation. Similar to non-selected MCL patients,most patients had disseminated disease and an adverseclinical course. Five specimens showed pleomorphicblastoid morphology and blastoid transformation was

associated with a change in phenotype, including gainor loss of CD10. Additional phenotypic variations likelyto cause diagnostic difficulty were present in eightspecimens: five were CD5) and five (all CD10+)expressed Bcl-6. One Bcl-6+ case carried a BCL-6translocation and three others had extra copies of theBCL-6 gene. Sequence analysis of the immunoglobulinheavy chain variable region in five cases showed onlyone to have low-level somatic mutation, indicating thatthey did not arise from germinal centre B cells.Conclusions: Expression of CD10 by MCL is oftenassociated with other variant morphological, immuno-phenotypic or genetic features, but does not reflectderivation from germinal centre B cells.

Keywords: Bcl-6, CD10, genetics, immunohistochemistry, mantle cell lymphoma

Abbreviations: FISH, fluorescence in situ hybridization; IGVH, immunoglobulin heavy chain variable; MCL, mantlecell lymphoma

Introduction

Mantle cell lymphoma (MCL)1–4 is a relatively well-defined type of non-Hodgkin’s lymphoma that typicallypresents with disseminated disease and pursues anaggressive clinical course. Most MCLs are neoplasms ofsmall centrocyte-like B cells with a characteristicCD20+ CD5+ CD43+ CD10) Bcl-6) CD23) immuno-phenotype. The majority lack significant somatichypermutation of immunoglobulin genes and are

thought to derive from naive, pre-germinal centre,mantle zone B lymphocytes.5–8 MCLs share a commonmolecular pathogenesis, associated in virtually all caseswith overexpression of the cell cycle regulatory proteincyclin D1 as a result of the t(11;14)(q13;q32) ⁄ CCND1-IGH translocation.1,9,10 Amongst the small B-cell lym-phomas, the detection of cyclin D1 expression is highlyspecific for, and the presence of the t(11;14)(q13;q32) isvirtually pathognomonic of, MCL.8,11–13

Despite these rather uniform typical features, it isnow recognized that MCLs display both clinical andbiological heterogeneity, which can cause difficulty inboth management and diagnosis. Several morphologi-cal variants are recognized, including lymphoblast-like

Address for correspondence: Ulises Zanetto, Department of Pathology,

City Hospital, Dudley Road, Birmingham B18 7QH, UK.

e-mail: ulises.zanetto@swbh.nhs.uk

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Limited.

Histopathology 2008, 53, 20–29. DOI: 10.1111/j.1365-2559.2008.03060.x

and pleomorphic blastoid variants, which may beassociated with additional genetic changes and anadverse prognosis.1,3,14–16 Recently, several studieshave demonstrated that approximately 15–30% ofMCLs show somatic mutation of immunoglobulinheavy chain variable (IGVH) genes, raising the possi-bility that these may derive from germinal centreor post-germinal centre B cells rather than naive Bcells.5–8 Variation from the typical immunophenotypeis also recognized. Up to 10% of cases lack expressionof CD5 detectable by immunohistochemistry and ⁄ orflow cytometry.17,18 A recent study has reported fivecases expressing the germinal centre protein Bcl-6 inassociation with genetic abnormalities of the BCL-6gene.19 In addition, rare cases of MCL have beenshown to express the germinal centre proteinCD10.20–22 The significance and clinicopathologicalassociations of such infrequent variant immunopheno-types are largely unknown.

In the present study 13 cases of MCL with aberrantexpression of CD10 were investigated. The clinical,morphological, immunophenotypic and genetic fea-tures of these cases are described, highlighting featuresof importance to diagnostic histopathologists. Weexamine the possibility that expression of CD10 mightreflect a germinal centre origin for these cases byanalysis of IGVH gene mutation.

Materials and methods

case material, immunophenotyping and

fluorescence in s itu hybridization

Seventeen specimens from 13 patients were identifiedfrom the archives of the authors’ institutions. Four ofthe cases were included (but not extensively described)in a previous series of CD5+ CD10+ B-cell lympho-mas.21 In each case, the diagnosis of MCL was made onclinical, histological, immunophenotypic and geneticfeatures according to the World Health OrganizationClassification of Tumours of Haematopoietic and Lymph-oid Tissues.2 Immunohistochemistry, flow cytometricimmunophenotyping and fluorescence in situ hybridiza-tion (FISH) were performed during routine diagnosticwork-up of the cases. In all cases, immunohisto-chemistry was performed on paraffin sections followingheat-mediated antigen retrieval using the streptavidin–immunoperoxidase method with diaminobenzidinechromogen, according to standard procedures. In sixcases multicolour flow cytometric immunophenotypingwas also performed using standard techniques. FISHusing dual-colour dual-fusion CCND1-IGH, IGH-BCL-2probes and BCL-6 dual-colour break-apart probes was

performed in 10, five and seven cases, respectively,according to standard procedures.

igvh

mutational analys is

DNA was extracted from paraffin sections using theQIAmp DNA Mini kit (Qiagen, Crawley, UK) and itsquality assessed using the BIOMED-2 control geneprimer set.23 Five of the eight cases tested yielded DNAof sufficient quality for assessment of IGH generearrangement. Rearranged IGH genes were amplifiedusing the BIOMED-2 IGVH FR1-JH primer set23 and theproducts visualized by electrophoresis through a 7%polyacrylamide gel. A single clonal product was seen ineach case. This was excised and DNA was purifiedusing the Qiaquick Gel Extraction kit (Qiagen). PurifiedDNA was directly sequenced using the consensus JH

primer and the ABI dRhodamine Terminator CycleSequencing kit (Applied Biosystems, Warrington, UK)on an ABI 377 Automated DNA Sequencer (AppliedBiosystems). IGVH gene usage and mutation statuswere determined by comparison with germ-linesequences using VBASE 2 and IMGT online databases.Cases with less than the standard threshold of 98%germ-line homology were considered to show IGVH

somatic mutation.

Results

clinical features

The clinical details of the patients studied are summa-rized in Table 1. There were eight men and five women,with a median age of 67 years (range 53–93 years).Most patients presented with multiple lymphadenopa-thy with or without splenomegaly and the bone marrowwas involved in each of the five cases in which the resultof bone marrow investigation is known. One patienthad a primarily leukaemic presentation and, in all, fiveof the 13 patients had peripheral blood involvement.Details of treatment and outcome were available for sixpatients. Five patients received multi-agent chemother-apy, four with Rituximab and one was not treated dueto comorbidity. One patient had progressive primaryrefractory disease and three progressed or relapsedfollowing initial responses to therapy (1–4 years fromdiagnosis). At last follow-up, four of the six patients haddied (0 months to 4 years from diagnosis).

morphology

Table 1 also shows the morphological features of thecases studied. Biopsy material from the time of first

CD10+ mantle cell lymphoma 21

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.

Tab

le1.

Clin

ical

,m

orp

holo

gic

al,

imm

unophen

oty

pic

and

gen

etic

feat

ure

sof

CD

10-p

osi

tive

man

tle

cell

lym

phom

a

Cas

eno.

Age

⁄se

xC

linic

alpre

senta

tion

BM

PB

Bio

psy

site

His

tolo

gy

Cyc

linD

1C

D5

CD

10

Bcl

-6FI

SHIG

VH

muta

tion

Ther

apy

Outc

om

e

1M

⁄75

Multip

lely

mphad

enopat

hy,

sple

nom

egal

y,bone,

CSF

Pos

Pos

Tes

tis,

skin

Typ

ical

Pos

Pos

Pos

Neg

IGH

-CC

ND

1Pos

IGH

-BC

L-2

Neg

Unm

uta

ted

(VH5-5

1)

Poly

-ch

emoth

erap

yPro

gre

ssiv

edis

ease

.D

OD

at6

month

s.C

onju

nct

iva

(2m

onth

sla

ter)

Ple

om

orp

hic

bla

stoid

Pos

Neg

Pos

Neg

BC

L-6

2co

pie

s

2F

⁄73

Multip

lely

mphad

enopat

hy

?N

egC

ervi

calLN

(at

pre

senta

tion)

Typ

ical

Pos

Pos

Neg

Neg

IGH

-CC

ND

1Pos

IGH

-BC

L-2

Neg

Unm

uta

ted

(VH5-5

1)

R-C

HO

PR

elap

seat

2ye

ars.

Furt

her

R-C

HO

P.

Die

dof

sepsi

s.

Soft

tiss

ue,

arm

(at

rela

pse

)Ple

om

orp

hic

bla

stoid

Pos

Neg

Pos

Neg

BC

L-6

3co

pie

s

3F

⁄72

Multip

lely

mphad

enopat

hy

?N

egA

xilla

ryLN

Ple

om

orp

hic

bla

stoid

Pos

Pos

Pos

Pos

IGH

-CC

ND

1Pos

x3IG

H-B

CL-2

Neg

BC

L-6

3-5

copie

s

Unm

uta

ted

(VH3-1

5)

Unkn

ow

nU

nkn

ow

n

4M

⁄68

Multip

lely

mphad

enopat

hy

?N

egR

etro

per

itonea

lLN

Typ

ical

Pos

Pos

Pos

Pos

IGH

-CC

ND

1Pos

BC

L-6

tran

sloca

tion

n⁄d

Unkn

ow

nU

nkn

ow

n

5F

⁄76

Ches

tw

allm

ass

?N

egC

hes

tw

all

mas

sTyp

ical

Pos

Pos

Pos

Neg

n⁄d

n⁄d

Unkn

ow

nU

nkn

ow

n

6M

⁄67

Cer

vica

lly

mphad

enopat

hy

?N

egC

ervi

calLN

Typ

ical

Pos

Pos

Pos

Neg

n⁄d

n⁄d

Unkn

ow

nU

nkn

ow

n

7M

⁄54

Multip

lely

mphad

enopat

hy

?Pos

Cer

vica

lLN

Typ

ical

Pos

Pos

Pos

Neg

IGH

-CC

ND

1Pos

n⁄d

Unkn

ow

nU

nkn

ow

n

8F

⁄63

Phar

yngea

lm

ass

?N

egPhar

yngea

lm

ass

Typ

ical

Pos

Pos

Pos

Neg

n⁄d

n⁄d

Unkn

ow

nU

nkn

ow

n

9M

⁄65

Multip

lely

mphad

enopat

hy,

sple

nom

egal

y

Pos

Pos

Axi

llary

LNTyp

ical

Pos

Neg

Pos

Wea

kPos

IGH

-CC

ND

1Pos

IGH

-BC

L-2

Neg

BC

L-6

5-8

copie

s

Low

leve

lm

uta

tion

(VH3-3

0)

FCR

CR

(1ye

ar)

22 U Zanetto et al.

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.

Tab

le1.

(Conti

nued)

Cas

eno.

Age

⁄se

xC

linic

alpre

senta

tion

BM

PB

Bio

psy

site

His

tolo

gy

Cyc

linD

1C

D5

CD

10

Bcl

-6FI

SHIG

VH

muta

tion

Ther

apy

Outc

om

e

10

M⁄5

8Le

uka

emia

Pos

Pos

Bone

mar

row

(at

pre

senta

tion)

Typ

ical

Pos

Pos

Neg

n⁄d

IGH

-CC

ND

1Pos

Faile

dPoly

-ch

emoth

erap

y,ritu

xim

ab

Pro

gre

ssio

n(B

M⁄P

B)

at4

year

s.D

OD

7m

onth

sla

ter

des

pite

auto

-BM

T.

Bone

mar

row

(at

pro

gre

ssio

n)

Ple

om

orp

hic

bla

stoid

Pos

Neg

Pos

n⁄d

11

F⁄6

2M

ultip

lely

mphad

enopat

hy,

sple

nom

egal

y

Pos

Pos

Bone

mar

row

(at

pre

senta

tion)

Typ

ical

Pos

Pos*

Pos

Neg

IGH

-CC

ND

1Pos

Faile

dPoly

-ch

emoth

erap

y,ritu

xim

ab

LNre

lapse

at12

month

s.A

live

at14

month

s.LN

(at

rela

pse

)Ple

om

orp

hic

bla

stoid

Pos

Pos

Neg

Neg

12

M⁄9

3M

ultip

lely

mphad

enopat

hy

n⁄d

Neg

Axi

llary

LNTyp

ical

Pos

Neg

Pos

Wea

kPos

IGH

-CC

ND

1Pos

IGH

-BC

L-2

Neg

BC

L-6

2co

pie

s

Unm

uta

ted

(VH3-1

1)

None

Die

dof

IHD

bef

ore

trea

tmen

t.

13

M⁄5

3M

ultip

lely

mphad

enopat

hy

Pos

Neg

Bone

mar

row

Typ

ical

Pos

Pos

Pos

Pos

IGH

-CC

ND

1Pos

BC

L-6

3-5

copie

sFa

iled

Unkn

ow

nU

nkn

ow

n

*C

D5

neg

ativ

eby

imm

unohis

toch

emis

try,

CD

5posi

tive

by

flow

cyto

met

ry.

BM

,bone

mar

row

;PB,

per

ipher

alblo

od;

FISH

,fluore

scen

cein

situ

hyb

ridis

atio

n;

CSF

,ce

rebro

spin

alfluid

;Pos,

posi

tive

;N

eg,

neg

ativ

e;D

OD

,die

dof

dis

ease

;LN

,ly

mph

node;

R-C

HO

P,

ritu

xim

ab,

cycl

ophosp

ham

ide,

doxo

rubic

in,

vincr

istine,

pre

dnis

olo

ne;

FCR

,fludar

abin

e,cy

clophosp

ham

ide,

ritu

xim

ab;

CR

,co

mple

tere

sponse

;BM

T,

bone

mar

row

tran

spla

nt;

IHD

,is

chae

mic

hea

rtdis

ease

.

CD10+ mantle cell lymphoma 23

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.

diagnosis was available in all cases. In 12 suchspecimens, the neoplastic infiltrate showed the typicalcytomorphology of MCL: small to medium-sized cen-trocyte-like cells with irregular nuclear outlines,slightly clumped chromatin and inconspicuous nucleoli(e.g. Figure 1). In lymph node and extranodal biopsyspecimens the lymphomas had a nodular and ⁄ ordiffuse growth pattern; in bone marrow trephinespecimens neoplastic cells formed predominantly non-paratrabecular lymphoid aggregates. In one initialdiagnostic specimen the lymphoma comprised a diffuseinfiltrate of cells with pleomorphic blastoid morphol-ogy: a heterogeneous population of medium-sizedand ⁄ or large cells with moderately condensed chro-matin, one or more small but readily visible nucleoli,and scanty cytoplasm (Figure 2).

In four cases a second biopsy specimen was takenduring the course of disease progression or at relapse.In each of these cases, although the original diagnostic

specimen had shown typical MCL morphology, thesubsequent specimen showed pleomorphic blastoidmorphology as described above (e.g. Figure 3). Thus,overall, pleomorphic blastoid morphology was shown byfive of 17 (29%) specimens from five of 13 (38%) patients.

immunophenotype

Immunohistochemistry (see Table 1) showed all spec-imens to express cyclin D1 with a nuclear pattern ofimmunoreactivity, in keeping with the diagnoses ofMCL. All MCLs except one expressed CD20. Thisspecimen was taken following rituximab therapy,known to induce CD20 negativity in mature B-celllymphomas.24 At first diagnosis, nine cases had aCD5+ CD10+ immunophenotype (e.g. Figure 2), twowere CD5) CD10+ (e.g. Figure 1), and two expressedCD5 but were CD10) at this stage of their evolution(e.g. Figure 3). CD43 was expressed by 10 of 12 cases

H&E Cyclin D1

CD5 CD10

Figure 1. Case 12. H&E-stained sections show the typical centrocyte-like morphology of mantle cell lymphoma. Immunohistochemistry shows

the neoplastic cells to express cyclin D1 and CD10, but not CD5. Scattered CD5+ T cells are present.

24 U Zanetto et al.

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.

studied, and Bcl-2 by nine of 11 cases. One case (case10) showed partial and dim expression of CD23 by flowcytometry but not by immunohistochemistry; CD23was not expressed by any other case. Three of 12 casesexamined showed strong nuclear positivity for Bcl-6 inthe majority of neoplastic cells (e.g. Figure 2); in twofurther cases there was weak expression of Bcl-6 byapproximately 50% of cells. These specimens were allCD10+, but included specimens with both pleomorphicblastoid and typical morphology and specimens bothpositive and negative for CD5. The five cases examinedfor expression of IgD were all positive. Where flow

cytometry was performed, this was concordant withthe immunohistochemistry, except in one specimen inwhich staining for CD5 was negative by immuno-histochemistry and positive by flow cytometry (case 11,considered CD5+ in this study).

Immunophenotyping was also performed on the fourfollow-up specimens available. In each, the changefrom typical to pleomorphic blastoid morphology wasaccompanied by an alteration in phenotype. In oneCD5+ CD10+ case (case 1) there was loss of CD5 inthe second specimen, and in another (case 11) therewas loss of CD10 in the second specimen. In two

H&E Cyclin D1

CD10

CD5

Bcl-6 BCL-6 FISH

Figure 2. Case 3. H&E-stained sections show the lymphoma cells to have pleomorphic blastoid morphology. Immunohistochemistry shows the

neoplastic cells to express cyclin D1, CD5, CD10 and Bcl-6. Fluorescence in situ hybridization using a dual-colour BCL-6 break-apart probe shows

three to five copies of BCL-6 without evidence of a BCL-6 translocation.

CD10+ mantle cell lymphoma 25

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.

CD5+ CD10) cases (cases 2 and 10), the secondspecimen showed a CD5) CD10+ immunophenotype(e.g. Figure 3). In case 10, flow cytometric immuno-phenotyping showed progressive accumulation ofCD10+ CD5) B cells in the peripheral blood in theperiod between the two bone marrow trephine biopsyspecimens. In total, CD5 negativity was shown by fiveof 17 (29%) specimens, three of which showed pleo-morphic blastoid morphology, from five of 13 (38%)patients. Expression of the other antigens tested,including cyclin D1 and Bcl-6, remained unchangedbetween specimens taken at presentation and atrelapse.

molecular genetics

The results of the molecular studies undertaken arealso presented in Table 1. FISH for the t(11;14)(q13;q32) ⁄ CCND1-IGH translocation was performed

in the diagnostic specimens of 10 of the 13 cases. Inkeeping with the diagnoses of MCL, each showed signalpatterns consistent with the presence of a CCND1-IGHtranslocation. The translocation was also detected inthe three follow-up specimens tested. Because theaberrant expression of Bcl-6 seen in five of the casescould be due to abnormalities of the BCL-6 gene, theseand two Bcl-6) cases (cases 1 and 2) were assessed byFISH using a BCL-6 break-apart probe. Of the caseswith Bcl-6 protein expression, one (case 4) showed atranslocation involving BCL-6 (and also evidence of anIGH translocation in addition to CCND1-IGH, suggest-ing the presence of a BCL-6)IGH translocation), three(cases 3, 9 and 13) showed multiple (three to eight)signals consistent with extra copies or amplification ofBCL-6 (e.g. Figure 2), and one (case 12) showednormal signals. One of the two Bcl-6) cases (case 2)also showed three copies of BCL-6. FISH for IGH-BCL-2was negative in all five cases examined.

H&E

2nd Biopsy

1st Biopsy

H&E

Cyclin D1

Cyclin D1 CD5

CD10

CD10

CD5

Figure 3. Case 2. H&E-stained sections from the first diagnostic biopsy (‘‘1st biopsy’’) show the typical morphology of mantle cell lymphoma.

Immunohistochemistry of this specimen shows the neoplastic cells to express cyclin D1 and CD5, but not CD10. A germinal centre shown is

negative for cyclin D1 and CD5, but positive for CD10. H&E-stained sections from a biopsy at relapse (‘‘2nd biopsy’’) show transformation to

pleomorphic blastoid morphology. Immunohistochemistry of this biopsy specimen shows that the neoplastic cells now express cyclin D1 and

CD10, but not CD5.

26 U Zanetto et al.

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.

To determine whether expression of CD10 by theseMCLs might reflect their derivation from germinalcentre B cells with somatic hypermutation of immuno-globulin genes, the sequences of the variable regions ofthe clonal rearranged IGH genes from five cases wereanalysed. Two cases utilized VH5-51 and one eachutilized VH3-11, VH3-15 and VH3-30. Four cases hadunmutated IGVH genes (using the accepted cut-offvalue of 98% germ-line homology) with 98.7–100%germ-line homology; the fifth showed low-level muta-tion of IGVH (97.4% germ-line homology). Attempts toanalyse three additional specimens (bone marrowtrephine biopsies) were unsuccessful. These resultssuggest that CD10+ MCLs are no different from othermantle cell lymphomas with regard to their IGVH

mutation status and do not suggest a germinal centrederivation for these tumours.

Discussion

Although MCLs are a relatively discrete group oflymphoid neoplasms with well-defined characteristicfeatures,1–4 it is clear that within this group there ismorphological, immunophenotypic and genetic varia-tion, the biological, diagnostic and clinical significanceof which is unclear. In this study we have described 13cases of MCL with aberrant expression of CD10. Despitethis unusual feature, all cases could be definitivelyidentified as MCLs by a combination of morphology, theexpression of cyclin D1, the remaining immunopheno-type and, most importantly, the detection of at(11;14)(q13;q32) translocation by FISH. The clinicalfeatures of these patients were similar to those of largerseries of unselected MCL patients:1–4 most presentedwith disseminated disease with or without peripheralblood involvement and, despite multi-agent therapy,outcome was generally poor.

Other studies have also documented aberrant expres-sion of CD10 by rare MCLs. Dong et al. have reported aseries of CD5+ CD10+ B-cell lymphomas, whichrepresented 0.4% of all B-cell lymphomas seen at onelarge diagnostic laboratory.21 Of these, one-quarterwere MCLs. In a flow cytometric study of 100 CD10+small B-cell lymphomas, Xu et al. identified a singleCD10+ MCL,22 and Camacho et al. included a CD10+MCL in their series, discussed in more detail below.19

Five of our specimens, including three pleomorphicblastoid tumours, showed a CD5) CD10+ phenotyperarely recognized before. Morice et al. have reported aleukaemic MCL with a CD5) CD10+ blastoid compo-nent,20 Yin et al. have reported a CD5) CD10+immunophenotype in a blastoid MCL and Kostopouloset al. have described a lymphoma with follicular

architecture, a CCND1 translocation detected by FISHand a CD5) CD10+ cyclin D1+ immunophenotype,consistent with an MCL.25 Such variant immunopheno-types can lead to considerable diagnostic difficulty andpossibly misdiagnosis of MCLs as follicular lymphoma,atypical CD10+ chronic lymphocytic leukaemia ⁄ smalllymphocytic lymphoma or even, in the case of blastoidtumours, diffuse large B-cell lymphoma or lymphoblas-tic lymphoma.21 Difficulties may be greatest whenassessing small needle core biopsy specimens or ‘‘fluid’’specimens by flow cytometry, when histological fea-tures helpful in diagnosis may be absent. Accuratediagnosis of cases such as these requires carefulintegration of morphological findings, a discriminatoryimmunophenotyping panel (including cyclin D1) and,increasingly, genetic findings.

Amongst our CD10+ MCLs, pleomorphic blastoidmorphology was seen in 29% of specimens. However,as the incidence of blastoid morphology varies fromapproximately 6% to approximately 26% in larger,unselected series of MCLs,3,26–28 analysis of additionalCD10+ MCLs will be required to ascertain if these twovariant features are linked. Interestingly, in all fourcases in which blastoid transformation of a previouslytypical MCL occurred, this transformation was accom-panied by an alteration in immunophenotype. In threecases there was loss of CD5 and in two of these therewas, in addition, gain of CD10 by a previously CD10)tumour. In one other case, CD10 expression was lostupon transformation. Similar immunophenotypicchanges were seen in two of the five cases of blastoidtransformation reported by Yin et al.29 The recognitionthat blastoid transformation of MCL may be accompa-nied by such phenotypic shifts has important impli-cations for the use of these markers in follow-upspecimens from MCL patients.

A further interesting finding of our study is that five(29%) of our specimens showed aberrant expression ofBcl-6, a transcription factor largely restricted duringB-cell differentiation to germinal centre B cells and thuscharacteristically found in B-cell lymphomas of germi-nal centre derivation. Bcl-6 protein expression was seenin both CD5+ and CD5) MCLs and in specimens withboth typical and blastoid morphology. Camacho et al.have recently reported a series of five Bcl-6+ MCLs, oneof which also expressed CD10.19 As these casesrepresented only 1.6% of all MCLs diagnosed in theirdepartment, our data suggests that Bcl-6 expressionmay be more frequent in CD10+ MCLs than amongstunselected cases. In diagnostic practice, cyclin D1immunohistochemistry and FISH for CCND1-IGH andIGH-BCL2 translocations may be necessary to distin-guish these cases from CD5+ follicular lymphomas.

CD10+ mantle cell lymphoma 27

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.

In the series of Camacho et al., four of the five casescarried translocations of BCL-6 with undisclosed part-ner genes and the remaining case had three copies ofthe BCL-6 gene.19 Similarly, in our study one Bcl-6+case contained a translocation of BCL-6 (probably withIGH), and three others showed extra copies or ampli-fication of BCL-6. It is possible therefore that Bcl-6expression in some of our cases is the result ofchromosomal alterations involving the BCL-6 gene,rather than a programmed expression of Bcl-6 resultingfrom a germinal centre origin of the lymphomas.However, the effect of BCL-6 translocations or copynumber increases on Bcl-6 expression is unclear. In therecent study of MCLs by Salaverria et al., gain ofchromosomal material at 3q27-28 detected by array-based comparative genomic hybridization was notassociated with increased expression of BCL-6 mRNAdetected by Lymphochip cDNA microarray.30 Similarly,although copy number gains and translocations ofBCL-6 are well recognized in other non-germinalcentre-derived lymphomas, such as activated B-cell-like diffuse large B-cell lymphomas, these often do notcorrelate with increased Bcl-6 protein or mRNAexpression.31 These genetic aberrations may insteadlead to functional dysregulation of BCL-6 expressionand potentially to altered expression of Bcl-6 targetgenes, without being associated with a detectableincrease in protein level. Furthermore, Bcl-6 expressionmay be regulated by additional mechanisms, such astranscriptional regulation and mutation of the BCL-6promoter,32 not studied in the present work.

The above discussion notwithstanding, as CD10positivity is a feature of both normal and malignantgerminal centre cells, the expression of CD10 didraise the possibility that this small subset of MCLsmight be derived from germinal centre cells. Likeother germinal centre-derived lymphomas, such MCLswould be expected to show evidence of somaticmutation of immunoglobulin genes. Indeed, someauthors have interpreted the detection of low-levelsomatic mutation of IGVH genes in up to 30% ofMCLs as evidence of a germinal centre orpost-germinal centre origin in these cases.6,33 How-ever, we found that only one of the five cases wesuccessfully examined showed significant somaticmutation, and this was at a lower level thantypically seen in germinal centre neoplasms.34 Thereis thus no evidence that CD10 expression by an MCLreflects a germinal centre derivation. Moreover,although the presence of IGVH mutation in someMCLs suggests the influence of antigen stimulationduring the development of these lymphomas, the lowlevel of mutation, the infrequent identification of

intraclonal variation and evidence of antigen selec-tion and the lack of immunoglobulin class switchingin these cases5–8,33,35,36 raise questions as to theprecise role of the germinal centre in this process.

Also known as membrane metallo-endopeptidase,CD10 is a cell surface neutral endopeptidase with anunknown role in lymphocyte biology. It is charac-teristically expressed by lymphoid populations with ahigh rate of apoptosis,37 suggesting a role in regu-lation of cell survival. However, the molecularpathogenesis of mantle cell lymphoma appears to bedominated by dysregulated cell proliferation ratherthan abnormal survival10 and both the mechanismof CD10 expression and its function on this smallsubset of MCLs remain unascertained. Nevertheless,an understanding of the expression of CD10 by MCLis important for diagnostic histopathologists. In thisstudy, we have shown in particular that CD10expression often occurs with other phenotypic vari-ations, may be induced or lost upon blastoid trans-formation and may be associated with geneticabnormalities of BCL-6 and Bcl-6 protein expression.There is no evidence from analysis of IGVH muta-tions that CD10+ MCLs derive from germinal centreB cells.

Acknowledgements

The authors are grateful to laboratory staff andhaemato-oncologists at their institutions for theircontribution to the diagnostic work-up of the casesand for provision of clinical data. We thank Dr HongtaoYe for help with additional FISH. C.M.B. is supported bya Senior Clinician Scientist Fellowship from The HealthFoundation, The Royal College of Pathologists andThe Pathological Society of Great Britain and Ireland.The Du lab is supported by The Leukaemia ResearchFund, UK.

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CD10+ mantle cell lymphoma 29

� 2008 The Authors. Journal compilation � 2008 Blackwell Publishing Ltd, Histopathology, 53, 20–29.