584 q 2000 Blackwell Science Ltd

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1 British Journal of Haematology 2000, 109, 584±591 Anaplastic large-cell lymphomas of B-cell phenotype are anaplastic lymphoma kinase (ALK) negative and belong to the spectrum of diffuse large B-cell lymphomas Eugenia Haralambieva, 1 Karen A. F. Pulford, 1 Laurence Lamant, 2 Stefano Pileri, 3 Giovanna Roncador, 1 Kevin C. Gatter, 1 Georges Delsol 2 and David Y. Mason 1 1 Leukaemia Research Fund Immunodiagnostics Unit, Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, Oxford, UK, 2 Department of Pathology and CIGH/CNRS, CHU Purpan, Toulouse, France, and 3 Section of Haemolymphopathological Histology, St. Orsola Polyclinic, Bologna, Italy Received 1 September 1999; accepted for publication 12 January 2000 Summary. There is controversy in the literature as to whether anaplastic large-cell lymphoma of B-cell phenotype is related to the t(2;5)-positive T- or `null' cell lymphoma of the same morphology. We report a study of 24 lymphomas with morphological features of anaplastic large-cell lymphoma which expressed one or more B-cell markers and lacked T-lineage markers. Clinical features were more in keeping with large B-cell lymphoma than with classical t(2;5)-positive anaplastic large-cell lymphoma, and immunostaining for anaplastic lymphoma kinase (ALK) protein provided no evidence for the (2;5) translocation (or one of its variants). The staining patterns for CD20 and CD79 were typical of diffuse large B-cell lymphoma, CD30 expression was variable, and most cases (15/22) lacked epithelial membrane antigen (EMA). These findings support the view that `B-cell anaplastic large-cell lymphoma' is unrelated to t(2;5)-positive (ALK-positive) lymphoma, and that it represents a morphological pattern occasionally encountered among diffuse large B-cell lymphomas. By the same reasoning, most tumours diagnosed as ÀLK-negative anaplastic large-cell lymphoma of T-cell or null phenotype' probably belong to the spectrum of peripheral T-cell lymphomas. Keywords: anaplastic large-cell lymphoma, B-cell markers, ALK protein, (2;5) translocation, diffuse large B-cell lymphoma. Anaplastic large-cell lymphoma was identified more than 15 years ago but clinical studies have been hampered by disagreement over the criteria for its diagnosis (Reiter et al, 1994; Massimino et al, 1995), in particular whether it is always of T-cell or `null' phenotype or whether B-cell tumours can also be included in this lymphoma category (Agnarsson & Kadin, 1988; Penny et al, 1991; Stein, 1993; Pileri et al, 1995). This disagreement is reflected by the inclusion of B-cell anaplastic large-cell lymphoma in the Kiel classification scheme (Lennert & Feller, 1992), but its exclusion from the REAL scheme (Harris et al, 1994). The identification of the (2;5)(p23;q35) chromosomal translocation and the cloning of the resulting nucleolar Correspondence: Professor David Y. Mason, Haematology Department, John Radcliffe Hospital, Oxford, OX3 9DU, UK. david.mason@cellsci.ox.ac.uk protein nucleophosmin±anaplastic lymphoma kinase (NPM±ALK) fusion gene (Morris et al, 1994) did not put an end to the controversies surrounding the definition of anaplastic large-cell lymphoma. Estimates of the frequency of the (2;5) translocation in anaplastic large-cell lymphoma have varied widely (Chan, 1996) and the phenotype of translocation-positive cases is also disputed, some groups report that all are of T-cell or `null' phenotype (Herbst et al, 1995; Wellmann et al, 1995; Lamant et al, 1996) whereas others have reported lymphomas of B-cell type carrying the (2;5) translocation (Downing et al, 1995; Arber et al, 1996; Weisenburger et al, 1996). Here, we address these questions by reviewing a series of lymphomas of B-cell phenotype with the classical morphological features of anaplastic large-cell lymphoma. Cases were investigated for expression of the ALK oncogene and also for anaplastic large-cell lymphoma markers, CD30 and 584 q 2000 Blackwell Science Ltd

2 epithelial membrane antigen (EMA). Our findings support the view that these tumours rarely, if ever, carry the (2;5) translocation and that they should be categorized as diffuse large B-cell lymphomas. This conclusion has clinically relevant prognostic implications. MATERIALS AND METHODS Cases and tissue samples. Biopsies of B-cell lymphomas from the surgical pathology files of the authors' institutions were reviewed to identify cases with the classical morphological features of anaplastic large-cell lymphoma (Agnarsson & Kadin, 1988). Clinical features. Patients' clinical records were reviewed to obtain basic data (for example sex, sites of involvement, overall survival). Immunohistochemical analysis. The following leucocyteassociated molecules were detected: CD3 (polyclonal antibody or monoclonal antibody 3D4), CD19 (antibody HD37), CD20 (antibody L26) (Mason et al, 1990), CD22 (antibody 4KB128), CD45 (antibody PD7/26), CD68 (antibody KP1) and CD79 (antibody JCB117) (Mason et al, 1995). Sections were also stained for molecules of relevance to the diagnosis of classical anaplastic large-cell lymphoma (Stein et al, 1985; Delsol et al, 1988; Falini et al, 1995): CD30 (antibodies BerH2 and Ki-1), EMA (antibody E29) and anaplastic lymphoma kinase (ALK) protein (monoclonal antibody ALK1; Pulford et al, 1997). In some cases, cytokeratin (antibody MNF116), CD15 (antibody By87a) and other appropriate markers were used to exclude other diagnoses (for example metastatic tumours, Hodgkin's disease). All antibodies were obtained from the authors' laboratories or from DAKO A/S, Glostrup, Denmark. Immunohistochemical analysis was performed by conventional streptavidin±biotin±peroxidase and APAAP techniques on paraffin-embedded tissue sections in all cases, and on cryostat tissue sections when fresh frozen material was available (Cordell et al, 1984; Pileri et al, 1997). Positive controls comprised normal and neoplastic tissues immunostained in parallel with the cases under investigation. Western blotting analysis. Proteins were extracted from one of the frozen tissue samples and subjected to Western blotting analysis for chimaeric 80 kda NPM±ALK protein, as described previously (Pulford et al, 1999), using the SU-DHL1 cell line as a positive control. RT-PCR analysis. Total RNA was extracted from 5-mmthick frozen sections of one of the tissue samples, and the detection of the NPM±ALK fusion transcript was performed as described previously (Lamant et al, 1996), using the SU-DHL1 cell line as a positive control. RESULTS Identification of cases of B-cell anaplastic large-cell lymphoma All cases fulfilled the morphological criteria for anaplastic large-cell lymphoma and expressed at least one B-lineage marker without evidence of the T-cell marker CD3. B-cell Anaplastic Large-cell Lymphoma 585 Clinical characteristics (Table I) The male±female ratio (13:11) was close to unity and the patients' ages ranged from 14 to 86 years (median 54 years). The disease often presented with lymphadenopathy (17 cases), but in seven patients there was extranodal disease with or without lymph node involvement. One patient (patient 4) had a history of Crohn's disease, but none had a record of a pre-existing lymphoproliferative disorder. Low-stage disease (I or II) at diagnosis was seen in 9/15 patients and high-stage disease (III or IV) in 6/15. Half of the patients reported systemic `B' symptoms. Response to therapy and overall survival are also summarized in Table I. Histological features The growth pattern typical of anaplastic large-cell lymphoma was seen in all cases studied, including localization within lymph node sinuses (Fig 1A), an apparently cohesive tumour cell proliferation (Fig 1B) (creating clusters or large masses of neoplastic cells) and partial preservation of underlying lymphoid tissue (Fig 1C) (i.e. lymphoid follicles and/or large groups of normal small lymphocytes), features which enhanced the typical `metastasis-like' appearance of the tumour. These characteristics tended to be most evident when the tumour cells were picked out in the tissue section by immunostaining for B-cell markers (Fig 1A and C). In all cases, the neoplastic cells showed the morphological features characteristic of anaplastic large-cell lymphoma (Agnarsson & Kadin, 1988; Penny et al, 1991; Stein, 1993; Pileri et al, 1995), namely large polymorphic cells with abundant cytoplasm containing irregularly shaped nuclei with coarse chromatin and one or more eosinophilic nucleoli. Bi- and multinucleated tumour cells were detected in all cases (Fig 1D): in some, they were numerous, with a Reed±Sternberg-like or horseshoe nuclear appearance; in others, they could be found only after careful morphological examination. A high mitotic rate and atypical mitoses were a frequent finding, as were apoptotic bodies and single necrotic cells (Fig 1D). Large necrotic areas were found in one of the samples. Immunophenotyping (Table II) In 18 of the 19 cases tested for the two B-cell markers detectable in paraffin sections (CD20 and CD79), both markers were expressed, although CD20 positivity was usually found in a peripheral `membrane-like' pattern outlining the borders of the tumour cells, whereas CD79 was expressed strongly within the cytoplasm (Fig 1E) often accentuating the irregular nuclear outline. In many samples, some degree of heterogeneity in the intensity of CD20 and CD79a expression by tumour cells was noted, and in four tumours partial antigen loss was observed. All the tumours tested (22 cases) were negative for ALK protein, the hallmark of lymphomas carrying the (2;5) translocation, when paraffin-embedded samples were immunostained. A single case (patient 7) showed weak to moderate staining of neoplastic cells with anti-alk in cryostat sections, but there was no reactivity in paraffin sections, no evidence for NPM±ALK protein by Western

3 586 E. Haralambieva et al Table I. Clinical data on B-cell lymphoma of anaplastic large-cell morphology. Case Sex Age Sites of initial involvement Stage Systemic `B' symptoms Therapy Response Survival (months) 1 M 38 Lymph nodes NI NI NI NI Died (60) 2 F 45 Lymph nodes, spleen, bones IV Present CT; RT CR Alive (126) 3 F 75 Lymph nodes I Absent CT; RT CR, CNS relapse Died (37) 4 F 79 Lymph nodes, colon IV Present CT; RT No response Died (1) 5 F 53 Tonsil I Present CT CR Alive (96) 6 M 60 Testis I Absent CT CR Alive (60) 7 M 48 Lymph nodes III Absent CT; RT CR Alive (72) 8 F 27 Post-nasal space I Absent CT CR Alive (65) 9 M 54 Lymph nodes II Present CT; RT No response Died (9) 10 M 36 Lymph nodes III Present CT PR Alive (2) 11 M 61 Lymph nodes II Present CT CR Alive (18) 12 F 69 Lymph nodes NI NI NI NI NI 13 M 24 Lymph nodes NI NI NI NI NI 14 M 68 Lymph nodes NI NI NI NI NI 15 F 23 Lymph nodes NI NI NI NI NI 16 M 28 Lymph nodes I Absent CT; RT CR Alive (36) 17 M 86 Lymph nodes NI NI CT No response Died (14) 18 M 79 Lymph nodes NI NI NI NI NI 19 F 74 Lymph nodes I Absent CT CR Alive (26) 20 F 73 Lymph nodes III Present CT CR Alive (96) 21 M 14 Lymph nodes NI NI NI NI NI 22 F * Lymph nodes NI NI NI NI NI 23 M 49 Ileocaecum I NI CT CR Alive (12) 24 F 85 Retroperitoneal space IV NI CT PR Alive (12) *Patient 22 was a paediatric case, but the exact age was not available. CR, complete response; CT, combination chemotherapy; NI, no information available; PR, partial response; RT, radiotherapy. blotting analysis and no NPM±ALK transcripts could be identified by RT-PCR. The pattern of CD30 expression ranged from clear expression by the majority of neoplastic cells in 11 cases, through seven cases with heterogeneous expression, to six clearly negative cases (Fig 1F). In only three cases was EMA [a marker frequently found in t(2;5)-positive anaplastic large-cell lymphoma of T or `null' type] expressed on the majority of neoplastic cells. In a further four cases, scattered EMA-positive cells were found, and the remaining 15 lymphomas tested were EMA negative (Table II). DISCUSSION Four clinically orientated studies of anaplastic large-cell lymphoma have been reported (Shulman et al, 1993; Clavio et al, 1996; Zinzani et al, 1996; Tilly et al, 1997), comprising a total of 320 cases, and each series contained a substantial number of `B-cell anaplastic large-cell lymphomas', with an overall frequency of 29%. This diagnosis is therefore made regularly in many centres (despite its absence from the REAL or the forthcoming WHO classification), and we assume that the 24 cases in the present study are representative of tumours categorized in this way. All cases tested were negative for ALK protein when stained in paraffin sections, in contrast to the high frequency of positive immunostaining reactions in classic anaplastic large-cell lymphoma of T-cell or `null' phenotype (Pulford et al, 1997). This suggests that the classic NPM± ALK fusion gene (and its variants) are rarely, if ever, present in large B-cell lymphomas of anaplastic morphology. These results are in agreement with two studies in which no ALKpositive tumours of B-cell phenotype could be found when a large number of lymphomas were screened for ALK expression (Benharroch et al, 1998; Falini et al, 1998), with the very rare exception of CD30-negative `immunoblastic' lymphomas of B-cell phenotype (Delsol et al, 1997), which express full-length ALK protein. However, the present results conflict with a study in which five of 13 tumours diagnosed as B-cell anaplastic large-cell lymphoma were considered to be ALK positive (Gascoyne et al, 1999). Most of the lymphomas in this report showed strong and homogeneous expression of the two B-cell markers used in paraffin-embedded tissue (CD20 and CD79), and the patterns (cytoplasmic for CD79 and membrane associated for CD20) (Fig 1E) were typical of classic diffuse large B-cell lymphoma. Antigen loss by the neoplastic cells was not a common event (in contrast to high-grade T-cell lymphomas; Wood et al, 1993), with the practical implication that the B- cell phenotype of lymphomas of the type described here is not prone to false negativity. Anaplastic large-cell lymphomas of T or `null' type usually express CD30 and EMA (Stein et al, 1985; Agnarsson & Kadin, 1988; Delsol et al, 1988; Falini et al, 1995; Pileri et al, 1995), whereas in the present study these markers were often absent (or present on only a proportion of the cells).

4 B-cell Anaplastic Large-cell Lymphoma 587 Fig 1. Histological features of cases of `anaplastic large-cell lymphoma' expressing B-cell markers. (A) (Upper left) A sinus distended by tumour cells (between the arrowheads) is seen in a haematoxylin and eosin (H & E)-stained section (100). (Lower left) Intrasinusoidal tumour cells are revealed by immunocytochemical labelling for CD20 (250). (Right) The morphology of the intrasinusoidal tumour cells is seen in a highpower view (arrowheads indicate the sinus margin) (600). (B) Neoplastic cells showing a `cohesive' growth pattern (600). (C) Tumour cells infiltrating around a residual B-lymphoid area (asterisk) are seen in a H & E section (top) and after immunostaining for the B-cell marker CD79 (bottom) (75). The higher power views on the right (200) show (top) infiltrating tumour cells (between arrowheads) adjacent to the normal B cells and (bottom) the characteristic cytoplasmic pattern of CD79 expression. (D) Neoplastic cell morphology showing a large multinucleate cell (above), an abnormal mitosis (middle) and apoptotic cells (below) (600). (E) Immunostaining of a lymphoma for CD79 and CD20 shows differing patterns of neoplastic cell reactivity (surface membrane associated and cytoplasmic respectively) (300). (F) Three cases are shown, illustrating (from top to bottom) positive, intermediate and negative reactivity for CD30 (150). This was particularly true for EMA, emphasizing its value for categorizing anaplastic lymphomas. These immunohistopathological findings suggest that B- cell neoplasms of anaplastic large-cell morphology have nothing in common with the ÀLK-omas' defined by the presence of the (2;5) translocation, and that they represent one morphological extreme in the spectrum of large B-cell lymphomas. A reported series of six follicular lymphomas

5 588 E. Haralambieva et al Table II. Immunophenotype of B-cell lymphomas of anaplastic large-cell morphology. B-cell markers T-cell marker ALCL markers Case Tissue CD19 CD20 CD22 CD79a CD3 CD30 EMA ALK 1 Lymph node Pos NT Pos Pos Neg Pos NT NT 2 Lymph node Pos Pos Pos NT Neg Pos Neg NT 3 Lymph node Pos Pos Neg Pos Neg Pos Neg Neg 4 Lymph node Pos Pos Neg Pos Neg Neg Neg Neg 5 Tonsil Pos Pos Pos Pos Neg Neg/Pos Neg Neg 6 Testis Pos Pos Pos Pos Neg Pos Neg Neg 7 Lymph node Pos Pos Pos Pos Neg Neg Neg Neg* 8 Post-nasal space tumour NT Neg NT Pos/Neg Neg Pos Neg Neg 9 Lymph node Pos Neg/Pos Pos Neg/Pos Neg Neg Neg Neg 10 Lymph node NT Pos NT Pos Neg Pos/Neg Neg Neg 11 Lymph node NT Pos NT Pos Neg Neg Neg/Pos Neg 12 Lymph node NT Pos NT Pos Neg Neg/Pos Neg/Pos Neg 13 Lymph node NT Pos NT Pos Neg Neg/Pos Neg Neg 14 Lymph node NT Pos NT Pos Neg Neg/Pos Neg Neg 15 Lymph node NT Neg/Pos NT Neg/Pos Neg Pos Neg Neg 16 Lymph node NT Pos/Neg NT Pos/Neg Neg Neg Neg Neg 17 Lymph node NT Pos NT Pos Neg Pos/Neg Neg Neg 18 Lymph node NT Pos NT NT Neg Neg Pos Neg 19 Lymph node NT Pos NT NT Neg Pos Neg/Pos Neg 20 Lymph node NT Pos NT NT Neg Pos Neg/Pos Neg 21 Lymph node NT Pos NT Pos Neg Neg/Pos Pos Neg 22 Lymph node NT Pos NT Pos Neg Pos Pos Neg 23 Ileocaecum NT Pos NT Pos Neg Pos NT Neg 24 Retroperitoneal tumour NT Pos NT Pos Neg Pos Neg Neg Pos/Neg, heterogeneous staining, with. 50% of cells positive; Neg/Pos, heterogeneous staining, with, 50% of cells positive. EMA, epithelial membrane antigen; NT, not tested (no frozen material or spare slides available). *See Results for further details of ALK immunostaining in this case. which transformed into anaplastic large-cell lymphomas of B-cell phenotype supports this view (Alsabeh et al, 1997). The clinical features of the cases in the present series also differed from those of classic t(2;5)-positive T- or `null' anaplastic large-cell lymphoma. The age distribution was essentially that of large B-cell lymphomas, none of the patients had a skin tumour and there was no preponderance of high-stage disease (Massimino et al, 1995; Tilly et al, 1997; Chan, 1998). Studies comparing large B-cell lymphomas of anaplastic and non-anaplastic morphology in terms of clinical outcome have yielded discrepant results (and none have included data on ALK protein expression or the NPM±ALK gene). In two studies, no difference in clinical course was found for a total of 34 anaplastic large-cell lymphomas (Noorduyn et al, 1994; Engelhard et al, 1997), whereas in a series from Tilly et al (1997) 56 anaplastic B-cell lymphomas showed better 5-year survival (more than 70%) than non-anaplastic diffuse B-cell neoplasms. Our own series is too small to resolve these discrepancies and more extensive clinical studies are needed to establish the relationship between anaplastic morphology and survival in B-cell lymphoma. In conclusion, the term `anaplastic large-cell lymphoma' appears at present to mean different things to different oncologists and pathologists. Some restrict its use to tumours which are of T or `null' phenotype (and which are likely to be of good prognosis), whereas others include B-cell neoplasms for which the prognostic pattern is less clear. Furthermore, when the term is used in the more restrictive fashion (i.e. excluding B- cell neoplasms), it is sometimes applied only to lymphomas of clearly anaplastic morphology (with the features seen in the present series, such as bizarre large cells), whereas other pathologists, using ALK immunostaining to detect cells carrying the (2;5) translocation and its variants, would include cases that are not obviously anaplastic in morphology. The scheme in Fig 2 shows how these conflicting elements can be reconciled. It not only shows `B-cell anaplastic largecell lymphoma' as a morphological pattern seen in diffuse large B-cell lymphoma but also incorporates the corollary that anaplastic large-cell lymphomas which are not of B-cell phenotype, but which lack ALK, may represent a morphological pattern seen in peripheral T-cell lymphoma. Whatever solutions to these questions emerge in the future, this diagram emphasizes the importance of shared understanding between oncologists and pathologists over the sense in which the diagnostic term `anaplastic large-cell lymphoma' is used. ACKNOWLEDGMENTS We are grateful to Susan Brunskill for help in providing clinical data. This work was supported by the Leukaemia

6 B-cell Anaplastic Large-cell Lymphoma 589 Fig 2. Schematic indication of how a diagnosis of `anaplastic large-cell lymphoma' may be related to underlying tumour entities. Many haematopathologists currently recognize three categories of large-cell lymphoma: (1) `diffuse large B-cell lymphoma'; (2) `anaplastic large-cell lymphoma' (subdivided into B-cell and `null'/t-cell subtypes); and (3) `peripheral T-cell lymphoma'. If ALK immunostaining is performed, other categories may also be recognized, e.g. ALK-negative anaplastic large-cell lymphoma. The results presented in this paper and elsewhere suggest that diffuse large B-cell lymphomas with anaplastic features should not be distinguished from other large B-cell neoplasms. This diagram illustrates this point and also suggests that ALK-negative anaplastic large-cell lymphomas with a T or `null' phenotype (which occur most commonly in adults) represent merely a morphological appearance seen in T-cell lymphomas. This scheme therefore indicates that ALKnegative large-cell lymphomas of anaplastic morphology, whether of B, T or `null' phenotype, should not be confused with ALK-positive lymphomas carrying the (2;5) translocation (or one of its variants), a recently recognized entity (Shiota & Mori, 1996; Benharroch et al, 1998; Falini et al, 1998) that occurs usually in younger patients, commonly has a cytotoxic T-cell phenotype (Foss et al, 1996; Krenacs et al, 1997) and is associated with a good prognosis. It should be added that this diagram does not include ALK-positive lymphomas of `small-cell' morphology (Kinney et al, 1993), which may be misdiagnosed as peripheral T-cell neoplasms but whose clinical features are likely to resemble those of other ALK-positive lymphomas. Research Fund (grants to E.H. and K.A.F.P.), L'Associazione Italiana per la Ricerca sul Cancro (AIRC) (grant to S.P.) and La Ligue Nationale Contre le Cancer & Projet Hospitalier de Recherche Clinique 1998 (grants to G.D. and L.L.). REFERENCES Agnarsson, B.A. & Kadin, M.E. (1988) Ki-1 positive large cell lymphoma. A morphologic and immunologic study of 19 cases. American Journal of Surgical Pathology, 12, 264±274. Alsabeh, R., Medeiros, L.J., Glackin, C. & Weiss, L.M. (1997) Transformation of follicular lymphoma into CD30-large cell lymphoma with anaplastic cytologic features. American Journal of Surgical Pathology, 21, 528±536. Arber, D.A., Sun, L.H. & Weiss, L.M. (1996) Detection of the t(2;5) (p23;q35) chromosomal translocation in large B-cell lymphomas other than anaplastic large cell lymphoma. Human Pathology, 27, 590±594. Benharroch, D., Meguerian-Bedoyan, Z., Lamant, L., Amin, C., BrugieÁres, L., Terrier-Lacombe, M.-J., Haralambieva, E., Pulford, K., Pileri, S., Morris, S.W., Mason, D.Y. & Delsol, G. (1998) ALKpositive lymphoma; a single disease with a broad spectrum of morphology. Blood, 91, 2076±2084. Chan, J.K.C. (1998) Anaplastic large cell lymphoma: redefining its morphologic spectrum and importance of recognition of the ALKpositive subset. Advances in Anatomic Pathology, 5, 281±313. Chan, W.C. (1996) The t(2;5) or NPM±ALK translocation in lymphomas: diagnostic considerations. Advances in Anatomic Pathology, 3, 396±399. Clavio, M., Rossi, E., Truini, M., Carrara, P., Ravetti, J.L., Spriano, M., Vimercati, A.R., Santini, G., Canepa, L., Pierri, I., Celesti, L., Miglino, M., Castellaneta, A., Damasio, E. & Gobbi, M. (1996) Anaplastic large cell lymphoma: a clinicopathologic study of 53 patients. Leukemia and Lymphoma, 22, 319±327. Cordell, J.L., Falini, B., Erber, W.N., Ghosh, A.K., Abdulaziz, Z., MacDonald, S., Pulford, K.A.F., Stein, H. & Mason, D.Y. (1984) Immunoenzymatic labeling of monoclonal antibodies using immune complexes of alkaline phosphatase and monoclonal anti-alkaline phosphatase (APAAP complexes). Journal of Histochemistry and Cytochemistry, 32, 219±229. Delsol, G., Al Saati, T., Gatter, K.C., Gerdes, J., Schwarting, R., Caveriviere, P., Rigal-Huguet, F., Robert, A., Stein, H. & Mason, D.Y. (1988) Coexpression of epithelial membrane antigen (EMA), Ki-1, and interleukin-2 receptor by anaplastic large cell lymphomas. Diagnostic value in so-called malignant histiocytosis. American Journal of Pathology, 130, 59±70. Delsol, G., Lamant, L., Pulford, K., Dastugue, N., Brousset, P., Rigal- Huguet, F., Al Saati, T., Cerretti, D.P., Morris, S.W. & Mason, D.Y. (1997) A new subtype of large B-cell lymphoma expressing the

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