CD5~ Small B-Cell Leukemias Are Rarely Classifiable as Chronic Lymphocytic Leukemia

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1 Hematopathology / CD5- LYMPHOPROLIFERATIVE DISORDERS CD5~ Small B-Cell Leukemias Are Rarely Classifiable as Chronic Lymphocytic Leukemia Jane C. Huang, M D, William G. Finn, M D, Charles L. Goolsby, PhD, Daina Variakojis, M D, and Do Ann C. Peterson, M D Key Words: CD5~; Chronic lymphocytic leukemia; Leukemic phase of non-hodgkin lymphoma; Splenic marginal zone lymphoma Expression of the CD5 antigen by neoplastic cells often is considered a diagnostic criterion for B-cell chronic lymphocytic leukemia (B-CLL). However, published series frequently include a number ofcd5~ cases. We studied the spectrum ofcd5~ B-cell lymphoproliferative disorders presenting with leukemic involvement and reassessed the prevalence ofcd5~ BCLL. We immunophenotyped 192 cases of clonal, small lymphocytic, B-cell disorders involving peripheral blood or bone marrow. Of these, 41 CD5~ cases were further analyzed, correlating the immunophenotypic findings with pathologic material and clinical data. Only 3 CDS' cases were classified as CD5~ B-CLL. These 3 cases had features unusual for B-CLL, including ight surface immunoglobulin expression, ight CD20 expression, and absence ofcd23 expression (2 cases) or Richter syndrome (1 case). The remainder of the CDS' cases consisted of hairy cell leukemia, hairy cell variant, prolymphocytic leukemia, follicular center cell lymphoma, lymphoplasmacytic lymphoma, splenic marginal zone lymphoma (SMZL), small lymphocytic lymphoma with marrow fiosis, and lymphoma, not further classified. Eight cases remained unclassified, but some displayed features of SMZL. CD5~ lymphoproliferative disorders of peripheral blood or bone marrow are unlikely to be CLL and often are classified more appropriately as non-hodgkin lymphoma in the leukemic phase. B-cell small lymphocytic leukemias are a heterogeneous group of diseases. Chronic lymphocytic leukemia (CLL) is by far the most common, but other disorders such as prolymphocytic leukemia (PLL), hairy cell leukemia, and leukemic phase of non-hodgkin lymphoma are also included in this group.' The various leukemic small B-cell disorders traditionally have been distinguished by morphologic and cytochemical features, but immunophenotyping has greatly aided the classification process. For example, CD5, a pan T-cell marker found in a subset of B lymphocytes, is characteristically expressed by CLL and mantle cell lymphoma but is generally absent in other B-cell neoplasms.2 In fact, the presence of CD5 is often a diagnostic criterion for CLL.3 Nevertheless, several published studies of CLL include a subpopulation of CD5" cases, as high as 36%.4~9 CD5" B-cell lymphocytic proliferations presenting in peripheral blood or bone marrow are less common than those expressing CD5 and may pose a diagnostic dilemma, particularly in patients without previous diagnoses. The objectives of this study were to characterize the spectrum of CD5", clonal Bcell, small lymphocytic disorders presenting in peripheral blood or bone marrow and to determine the prevalence of CD5~ B-cell CLL within this group of CD5" disorders. Materials and Methods From January 1993 to June 1997, from the files of the Flow Cytometry Laboratory at rthwestern Memorial Hospital, Chicago, 111, we identified 192 cases of clonal B-cell disorders presenting in peripheral blood or bone marrow. All cases demonstrated clonality by surface light chain restriction on B lymphocytes (CD19, CD20). Cases with prior lymph node or tissue diagnosis were excluded from the study. Of the 192 cases, 41 were CD5". The immunophenotypic features of 123 Abstract

2 Huang et al / CD5- LYMPHOPROLIFERATIVE DISORDERS these 41 cases were then correlated with all available morphologic studies and clinical history. Immunophenotyping by Flow Cytometry CD5 expression was ascertained by 2- or 3-color flow cytometric analysis with antibodies against CD5 and CD 19. Lack of CD5 expression on CD 19 cells was determined by comparison with the negative or nonreactive populations and, in some cases, with appropriate negative isotype Morphologic Evaluations Wright-stained peripheral blood smears were reviewed on all 41 CD5 cases. In addition to the bone marrow biopsy specimens in 32 cases, lymph node biopsy specimens in 8 cases and splenectomy specimens in 6 cases were reviewed. Cases were classified by consensus among 4 of us (J.C.H., W.G.F, D.V., L.C.P) at a multiheaded microscope, using diagnostic criteria according to the French-American-British guidelines2 and the Revised European-American Lymphoma classification." If tissue sections were not available, a case was classified as a splenic marginal zone lymphoma (SMZL) after clinicopathologic correlation, requiring compatible peripheral blood and bone marrow morphologic features,212 immunophenotypic findings, 13 and clinical data (ie, presence of splenomegaly). Clinical History and Follow-Up Presenting symptoms and physical findings, as well as additional laboratory and radiologic tests and available 2 1. : -. - E 4» " i * : >.* * ( x. '.!' *?* "" -.. ' " i i nil ' i Ml K Figure I I A, Dim or weak expression of surface immunoglobulin (sig). B, Bright/strong expression of sig. 124 Two- or 3-color immunophenotyping (combinations of antibodies labeled with fluorescein isothiocyanate, phycoerythrin, or phycoerythrin-cyanin 5) was performed as previously described,10 using various combinations of antibodies against the following antigens: CD5, CD 10, CD lie, CD 19, CD20, CD22, CD23, CD25, and K and X. light chains. Antibodies reactive to CD22 and CD23 were purchased from Immunotech (Westwood, Me); C D l l c and CD25 from Becton Dickinson (San Jose, Calif); a CD19-K-X combination from DAKO (Carpinteria, Calif); and CD5, CD 10, K, X, CD 19, and CD20 from Coulter Cytometry (Kendall, Fla). The peripheral blood or bone marrow specimens were prepared by a slightly modified protocol of the standard RBC Q Prep (Coulter Cytometry) lysis technique in which cells are washed after RBC lysis followed by the addition of antibodies and the fixation step. The immunophenotypic analyses were performed on a Coulter Epics Profile or Coulter XL flow cytometer, using 550-nm, 600-nm, and 650nm dichroic filters with 525-nm (fluorescein isothiocyanate) bandpass, 585-nm (phycoerythrin) bandpass, and 670-nm bandpass (phycoerythrin-cyanin 5) optical filters. controls (IgG2a) to measure the extent of nonspecific binding. For CD20 and surface immunoglobulin (sig), semiquantitative intensity of staining also was evaluated and was classified as ight or, representing high or low density of surface antigens, respectively. Strong or ight staining was noted if the fluorescence of the positive population did not overlap with that of the negative or nonreactive cell population, and weak or staining was noted if the intensity of staining in the positive group overlapped with the negative group I Figure II.

3 Hematopathology / ORIGIL ARTICXE follow-up, were obtained from the patients' physicians or medical charts. Results 10-i 8 8tl 6- HCL* CLL PLL FCL LPL SMZL NHL' UNC Figure 21 Distribution of the 41 CD5" B-cell disorders by diagnosis. The asterisk indicates 5 cases of HCL and 1 case of HCL variant; the dagger, 1 case of small lymphocytic lymphoma with marrow fiosis, and 2 cases of NHL, not otherwise specified. HCL = hairy cell leukemia; CLL = chronic lymphocytic leukemia; PLL = prolymphocytic leukemia; FCL = follicular center cell lymphoma; LPL = lymphoplasmacytic lymphoma; SMZL = splenic marginal zone lymphoma; NHL = other non-hodgkin lymphoma; UNC = unclassified. The 41 CD5" cases included 26 men and 15 women with a median age of 63 years (range, years). All cases presented with peripheral blood or bone marrow involvement. Clinical and laboratory data for the patients are shown in ITable II, as are the complete immunophenotypic results. IFigure 21 shows the overall distribution of the cases by diagnosis. Five cases were classified as hairy cell leukemia, 1 as hairy cell leukemia-variant, 3 as CLL, and 2 as PLL. Lymphomas with leukemic involvement included 9 cases of follicular center cell lymphoma, 4 of lymphoplasmacytic lymphoma, 6 of SMZL, 1 of small lymphocytic lymphoma with bone marrow fiosis, and 2 of lymphoma, not otherwise classified. Eight cases were unclassified. Five cases showed morphologic features characteristic of hairy cell leukemia in peripheral blood and bone marrow, and the malignant cells were positive for tartrate-resistant acid phosphatase.14 The immunophenotypic profile was also typical of hairy cell leukemia with coexpression of CD 19 and CD lie, as well as CD 19 and CD25. The morphologic features of the peripheral blood, bone marrow, and spleen specimens from the patient with hairy cell leukemia variant (patient 6) were similar to hairy cell leukemia except for the prominent nucleoli in many of the lymphoid cells. Immunophenotyping of the patient's peripheral blood specimen revealed expression of CD1 lc but absence of CD25. Only 3 of the 41 cases were classified as CLL. All 3 were elderly patients with peripheral absolute lymphocytosis and clinical evidence of organ involvement at the time of diagnosis (Table 1). In 2 of the 3 patients (patient 7 and 8), circulating lymphocytes were small and monotonous appearing with coarsely condensed chromatin and scant cytoplasm. The bone marrow pattern of involvement was diffuse in patient 8 and interstitial in patient 7. The lymphocytes in the bone marrow appeared uniform in size and appearance with coarse chromatin. However, the immunophenotypic profile was not typical for CLL.10 Specifically, in addition to the CD5 negativity, slg and CD20 expression were ight, and CD23 was negative in both cases. The peripheral blood lymphocytes in the third patient with CLL (patient 9) were mostly small to medium-sized with condensed chromatin but admixed with occasional prolymphocytes. In addition, the patient had 2 lymph node biopsy specimens showing histologic features of CLL with many proliferation centers I Image II. However, a bone marrow biopsy specimen that was obtained at the same time as the second lymph node biopsy showed large cell transformation, consistent with Richter syndrome. Immunophenotyping was performed on the second lymph Image I I A low-power view of the lymph node biopsy specimen from patient 9 shows diffuse effacement of nodal architecture with pale-appearing areas (H&E, x64). The pale areas represent proliferation centers rich in prolymphocytes (inset, H&E, x1,000), characteristic of B-cell chronic lymphocytic leukemia. AmJCIinPathol 1999;111:

4 Huang et al / CD5^ LYMPHOPROLIFERATIVE DISORDERS Table II Clinical and Immunophenotypic Features of 41 Cases of CD5" B-Cell Disorders Immunophenotype Clinical Features Patient./ Sex/Age (y) ALC Lymphadenopathy Hepatosplenomegaly 21) 23 Hairy cell leukemia 1/M/ /M/38 3/M/50 4/M/48 5/M/48 6/M/60* X- X- X- X- X- X Chronic lymphocytic leukemia 7/F/ /M/ /M/ K- K- Small lymphocytic lymphoma 10/M/ Prolymphocytic leukemia /M/78 12/M/ X- K- Follicular center cell lymphoma 13/M/ /M/ /F/ /M/ /F/ /F/ /F/75 20/F/ /M/ X- X- K- X- X- K- K- Lymphoplasmacytic lymphoma /F/60 23/M/ /F/ /M/ K- K- X- K- Splenic marginal 26/M/82 27/M/50 28/F/83 29/F/60 30/F/89 31/M/63 X- X- X- X- K- bi n-hodgkin lymphoma 32/F/ /M/ bi Unclassified 34/M/68 35/F/82 36/M/83 37/F/69 38/M/66 39/F/47 40/M/53 41/M/73 K- K- X- K- X- X- X- zone lymphoma Ik *h ALC = absolute lymphocyte count (xl09/l); sig = surface immunoglobulin; = not available; X = lambda light chain; = ight; - = negative; = positive; = not done; K = kappa light chain. * The diagnosis is HCL variant. 126

5 Hematopathology / ORIGIL ARTICLE the lymph node biopsy specimen in 1. Patient 22 did not have a serum paraprotein, but the other 3 patients had a monoclonal IgM protein. The lymphoma cells expressed CD22 in 3 of 3 cases and CD1 lc in 2 of 4 cases, but did not express CD23 in 3 of 3 cases or CD 10 in 4 of 4 cases. Six cases were classified as SMZL. All 6 patients presented with splenomegaly, and 2 of them had lymphadenopathy. All 6 had involvement of the peripheral blood and bone marrow at the time of diagnosis. In 3 of the cases, the lymphocytes had heterogeneous morphologic features llmage 31. A minority of the cells had coarsely condensed chromatin and scant cytoplasm. Other lymphocytes had distinct eccentric Two patients had PLL; absolute lymphocyte counts were between 28 and 30 x 109/L. The peripheral blood lymphocytes showed a single prominent nucleolus with chromatin condensation around the periphery. In both cases, the disease involved the bone marrow focally with an interstitial pattern of involvement. A splenectomy specimen from 1 patient confirmed the diagnosis of PLL. One of the patients with PLL had a limited immunophenotype, but lymphocytes in both patients were CD5" and expressed ight slg. Peripheral blood and bone marrow involvement by non-hodgkin lymphoma constituted the majority of the CD5~ cases. Nine cases were classified as follicular center cell lymphoma. All 9 of these cases had bone marrow involvement. Six of the 9 cases of follicular center cell lymphoma had elevated peripheral blood lymphocyte counts. Five cases with peripheral blood involvement showed variable proportions of deeply cleaved lymphocytes with scant cytoplasm. The cleaved lymphocytes constituted approximately 40% to 90% of the lymphoid cells. However, the circulating lymphocytes in the sixth patient with peripheral blood involvement (patient 21) were similar to CLL llmage 21 with rare to absent cleaved cells. The bone marrow biopsy specimen, similar to all others in this group, contained characteristic paratrabecular lymphoid aggregates. The diagnosis was confirmed by a subsequent lymph node biopsy in this and 3 other cases and by a subsequent splenectomy in 1 case. The immunophenotypes were variable, but all were CD5 and ight CD20. CD 10 expression was seen in 4 of 9 cases. All 4 cases of lymphoplasmacytic lymphoma involved the bone marrow, and 1 case (patient 24) also had peripheral blood involvement. The peripheral blood lymphocytes in patient 24 were morphologically mature-appearing. An interstitial or nodular pattern of bone marrow involvement was seen. Subsequent tissue examination showed lymphoplasmacytic lymphoma in spleen sections in 2 cases and in llmage 21 The peripheral blood lymphocytes from patient 21 displayed round nuclei with condensed chromatin, resembling chronic lymphocytic leukemia lymphocytes. However, bone marrow and lymph node biopsies confirmed a follicular lymphoma (Wright stain, x1,200). node biopsy specimen and not on the bone marrow specimen. Except for the lack of CD5 expression, the findings were typical for CLL. The lymphocytes expressed weak slg and CD20 and were positive for CD23. Patient 10 had a small lymphocytic lymphoma in the bone marrow specimen that was characterized by uniform small lymphocytes with round nuclei, condensed chromatin, and scant cytoplasm. The malignant lymphoid infiltrates were interstitial and nodular; none was paratrabecular. The morphologic features were compatible with CLL, but the patient did not have peripheral blood lymphocytosis. Only the bone marrow was immunophenotyped. Except for the lack of CD5 expression, the clonal B-cell population showed slg, CD20, and CD23 expression, features typical for CLL. Image 31 Peripheral blood lymphocytes from 3 of the 6 patients with splenic marginal zone lymphoma displayed a spectrum of morphologic appearances, including lymphocytes with irregular cytoplasmic borders (left), plasmacytoid lymphocytes (middle), and cleaved lymphocytes (right) (Wright stain, x1,200)

6 Huang et al / CDS- LYMPHOPROLIFERATIVE DISORDERS nucleoli and loosely condensed chromatin. Cytoplasmic irregularities imparting a villous appearance were occasionally present but were not a consistent feature. Occasional plasmacytoid lymphocytes and rare cleaved cells were seen. In contrast, the other 3 patients with SMZL (patients 26-28) had uniform monomorphous lymphocytes with abundant cytoplasm and frequent nucleoli. Eight cases were not classified. In 6 of the 8 unclassified cases, peripheral blood smears were the material available for review. The peripheral lymphocytes were not morphologically acceptable for CLL, but some resembled the lymphocytes in the SMZL cases. The lymphocytes were heterogeneous in 3 cases; many lymphocytes had eccentric nucleoli, and occasional plasmacytoid cells and small mature lymphocytes were present. The other 5 cases had more homogeneous lymphocytes with abundant cytoplasm and visible to prominent nucleoli. The immunophenotypic results included the following: ight slg expression Image 41 Photomicrograph of spleen from patient 31, who had splenic marginal zone lymphoma (H&E, x200). 128 Discussion Although CD5 expression in B-cell CLL is well documented 3 and is recognized in recent classification systems," 15 a number of cases reported as CLL or CLL variants are CD5".4"9'16,17 CD5" CLL, despite its persistence in diagnostic hematology, represented fewer than 2% of the 192 B-cell leukemias in the current study. Furthermore, each of the 3 cases classified as CD5 CLL had unusual features. Two patients had morphologic features of CLL in blood and bone marrow specimens, but the immunophenotypic findings were unusual for CLL with ight slg, ight CD20 expression, and absence of CD23. The third patient with CLL showed large cell transformation in the bone marrow specimen (Richter syndrome), despite lymph node histologic features and an immunophenotype typical for CLL except for the absence of CD5 expression. The majority of the CD5" small B-cell disorders in the present study represented non-hodgkin lymphoma in the leukemic phase, including follicular center cell lymphoma and lymphoplasmacytic lymphoma. Six cases were classified as SMZL, a provisional entity in the Revised European-American Lymphoma classification." In 3 of these cases, the peripheral blood lymphocytes had heterogeneous morphologic features. The other 3 cases displayed distinctive uniform lymphocyte morphologic features, with abundant cytoplasm and round to oval nuclei with coarse chromatin and small nucleoli. These cells in the latter 3 cases displayed morphologic features previously ascribed to a subtype of CLL 18 and were similar to the C D l l c B-cell chronic lymphoproliferative disorder described by Hanson et al.19 About half of the 14 patients in the series reported by Hanson et al19 were CD5", and some of these patients subsequently underwent splenectomies that revealed SMZL (Curtis Hanson, MD, personal communication by phone; summer 1996). The CDllc disorders and SMZL overlap, but the exact relationship is unknown. The bone marrow was focally involved by lymphoma in 5 of the 6 cases of SMZL. All 5 cases had focal, nonparatrabecular lymphoid infiltrates, but paratrabecular aggregates also were seen in 2 cases. In contrast, the sixth patient (patient 31) had diffuse bone marrow involvement. The lymphocytes in the bone marrow contained moderate amounts of cytoplasm, resulting in well-spaced nuclei. A lymph node biopsy and subsequent splenectomy I Image 41 in this patient confirmed the diagnosis of a SMZL. In addition to the CD5 negativity, slg expression was ight in 4 of 6 cases; CD20 expression was ight in 5 of 6 cases; CD23 was negative in 5 of 6 cases; CD22 was expressed in all 6 cases; and CD1 lc was positive in 3 of 6 cases. in 7 of 8 cases, ight CD20 in 8 of 8 cases, CD23" in 7 of 7, CD22 in 7 of 7 cases, CD 10" in 7 of 7 cases, CD1 lc in 3 of 8 cases, and CD25 in 7 of 8 cases. The 2 remaining patients had leukemic involvement by non-hodgkin lymphoma that could not be further subclassified. Patient 32 had no peripheral blood absolute lymphocytosis, but the bone marrow contained a small B-cell lymphoma with fiosis. Patient 33 had extensive disease with involvement of peripheral blood, bone marrow, spleen, liver, lymph nodes, pleural cavity, and cereospinal fluid. The lymph node morphologic features for patient 33 were suggestive of mantle cell lymphoma, but cytogenetic and molecular data did not confirm the bcl-\ translocation.

7 H e m a t o p a t h o l o g y / ORIGIL ARTICLE Published series of CLL report varying incidences of CD5" CLL, ranging from 0% to 36%. 4 " 10 We propose 2 causes for this variability. First, different studies have used different criteria to determine the status of CD5 expression. Expression of CD5 in CLL is heterogeneous and forms a spectrum of variable densities, similar to CD20 and slg expression.20 The status of CD5 expression in the present study was evaluated by comparing the surface fluorescence intensity of the clonal B-cell population with the intensity of the negative or nonreactive population and with appropriate negative isotype controls. Although this method is sensitive, the possibility of extremely low-density expression of CD5 could not be excluded. True absence of expression may be determined by molecular methods, such as the detection of CDS messenger R.21 Second, judging from the data we report, it is likely that many cases reported as CD5" CLL represent specific nonhodgkin lymphomas in the leukemic phase. This is difficult to confirm, since the diagnosis of CLL is based primarily on peripheral blood morphologic features and immunophenotype, and additional studies are not always undertaken. However, half of the cases in 1 report of follicular lymphoma in the leukemic phase were originally referred to as CLL.22 Furthermore, published reports associate atypical features with CD5~ CLL, including higher incidence of organomegaly, shorter survival, more advanced stage of disease, and atypical morphologic features.6'9,17'23 Finally, many reported cases of atypical CLL are associated with characteristics of nonhodgkin lymphoma, including the presence of circulating small cleaved lymphocytes and characteristic cytogenetic features, such as the t(14;18).17 In view of our findings and those of other investigators, we conclude that CD5" CLL is rare and is often more appropriately classified as non-hodgkin lymphoma in the leukemic phase. It follows, therefore, that CD5" B-cell leukemias presenting as CLL warrant a more extensive clinical and laboratory evaluation before a definitive diagnosis is made. Only after a non-hodgkin lymphoma or other chronic leukemic disorders have been excluded should a diagnosis of CD5~ CLL be considered. From the rthwestern University Medical School, Chicago, Illinois. Address reprint requests to Dr Peterson: Wesley Pavilion, Room 393, 250 E Superior St, Chicago, IL References 1. Kroft SH, Finn WG, Peterson LC. The pathology of the chronic lymphoid leukemias. Blood Rev. 1995;9: Bennett JM, Catovsky D, Daniel M-T, et al. Proposals for the classification of chronic (mature) B and T lymphoid malignancies. J Clin Pathol. 1989;42: Cheson BD, Bennett JM, Grever M, et al. National Cancer Institute-sponsored working group guidelines for chronic lymphocytic leukemia: revised guidelines for diagnosis and treatment. Blood. 1996;87: Batata A, Shen B. Immunophenotyping of subtypes of Bchronic (mature) lymphoid leukemia: a study of 242 cases. Cancer. 1992;70: Geisler CH, Larsen JK, Hansen NE, et al. Prognostic importance of flow cytometric immunophenotyping of 540 consecutive patients with B-cell chronic lymphocytic leukemia. Blood. 1991;78: Kurec AS, Threatte GA, Gottlieb AJ, et al. Immunophenotypic subclassification of chronic lymphocytic leukemia (CLL). Br J Haematol. 1992;81: Matutes E, Owusu-Ankomah K, Morilla R, et al. The immunological profile of B-cell disorders and proposal of a scoring system for the diagnosis of CLL. Leukemia. 1994;8: De Rossi G, Mauro FR, Lo Coco F, et al. CD5 negative lymphocytosis mimicking typical B-chronic lymphocytic leukemia: description of 26 cases. uv Rev Fr Hematol. 1993;35:45M Salomon-Nguyen F, Valensi F, Merle-Beral H, et al. A scoring system for classification of CD5" B CLL versus CD5 B CLL and B PLL. Leuk Lymphoma. 1995; 16:445^ Finn WG, Thangavelu M, Yelavarthi KK, et al. Karyotype correlates with peripheral blood morphology and immunophenotype in chronic lymphocytic leukemia. Am ] CUnPathoi 1996;105: Han-is NL, Jaffe ES, Stein H, et al. A revised EuropeanAmerican classification of lymphoid neoplasms: a proposal from the International Lymphoma Study Group. Blood. 1994;84: Melo JV, Hegde U, Parreira A, et al. Splenic B cell lymphoma with circulating villous lymphocytes: differential diagnosis of B cell leukaemias with large spleens. J Clin Pathol. 1987;40: Matutes E, Morilla R, Owusu-Ankomah K, et al. The immunophenotype of splenic lymphoma with villous lymphocytes and its relevance to the differential diagnosis with other B-cell disorders. Blood. 1994;83: Paoletti M, Bitter MA, Varan JW. Hairy cell leukemia: morphologic, cytochemical, and immunologic features. Clin LabUed. 1988;8: Jaffe ES, Berard CW, Dibold J, et al. Society for Hematopathology Program: Proposed World Health Organization classification of neoplastic diseases of hematopoietic and lymphoid tissues. Am J SurgPathol. 1997;21: The CD5" B-cell disorders were often difficult to classify accurately based solely on analysis of peripheral blood. In some cases, the diagnosis of lymphoma was reached after the absence of CD5 expression prompted further clinical and laboratory evaluation. For example, the peripheral lymphocytes of 1 patient (patient 21) morphologically resembled CLL (Image 2), but immunophenotyping revealed the lack of CD5 expression. A subsequent bone marrow biopsy revealed paratrabecular lymphoid infiltrates, and a subsequent lymph node biopsy was diagnostic of follicular small cleaved cell lymphoma. Cytogenetic study also revealed the characteristic t(14;18) in this case.

8 Huang et al / CD5" LYMPHOPROLIFERATIVE DISORDERS 16. Maloum K, Davi F, Magnac C, et al. Analysis of VH gene expression in CD5 and CD5~ B-cell chronic lymphocytic leukemia. Blood. 1995;86: Matutes E, Oscier D, Garcia-Marco J, et al. Trisomy 12 defines a group of CLL with atypical morphology: correlation between cytogenetic, clinical and laboratory features in 544 patients. Br j Haematol. 1996;92: Peterson LC, Bloomfield CD, Sundberg RD, et al. Morphology of chronic lymphocytic leukemia and its relationship to survival. Am J Med. 1975;59: Hanson CA, Gribbin TE, Schnitzer B, et al. CDllc (Leu-M5) expression characterizes a B-cell chronic lymphoproliferative disorder with features of both chronic lymphocytic leukemia and hairy cell leukemia. Blood. 1990;76: Kay NE, Peterson L. Heterogeneity of CD5 memane expression on B-chronic lymphocytic leukemia cells. Leu/c Lymphoma. 1991;5: Gignac SM, Buschle M, Hoffand AV, et al. Down-regulation of CD5 mr in B-chronic lymphocytic leukemia cells by differentiation-inducing agents. Eur] Immunol. 1990;20; Melo JV, Robinson DSF, de Oliveira MP, et al. Morphology and immunology of circulating cells in leukemic phase of follicular lymphoma. ] Clin Pathol. 1988;41: Criel A, Wlodarska 1, Meeus P, et al. Trisomy 12 is uncommon in typical chronic lymphocytic leukemias. Br J Haematol. 1994;87: Am J Clin Pathol 1999,111: