Hairy cell leukemia

The morphologic differential diagnosis of mature B-cell neoplasms with cytoplasmic projections includes splenic lymphoma with villous lymphocytes and hairy cell leukemia. Although the classification of hairy cell leukemia is not universally recognized, 3 variants have been described, namely, classic, variant, and Japanese variant, each of which has different clinical and immunophenotypic features. Classic hairy cell leukemia is virtually always CDI I c+, CD25+, and CD103+. Variant and Japanese variant hairy cell leukemias are usually CDI 1 c+, always CD25-, and occasionally CD103+. Each variant is characteristically CD1 0-. We present a case of hairy cell leukemia with a unique immunoprofile in that the cells were CD1 0+, CD25+, and CD103-, and we review the criteria helpful in differentiating "hairy" B-cell neoplasms. This case emphasizes the variability of hairy cell leukemia and the need to correlate all clinical and pathologic data in reaching a diagnosis.

(Arch Pathol Lab Med. 2000;124:1710-1713)

Splenic lymphoma with villous lymphocytes (SLVL) and hairy cell leukemia (HCL) are similar-appearing B-- cell neoplasms with cytoplasmic projections. Fortunately, HCL often has a characteristic immunoprofile, so that flow cytometry may assist in arriving at the correct diagnosis when correlated with all other available pathologic studies and clinical data. We present a case that clinically, morphologically, and cytochemically resembled classic HCL1 (HCL-C, typical HCL2), but that had an immunoprofile different from that of all previously described cases of HCL.

REPORT OF A CASE

A 79-year-old white American man who had never visited Japan presented to the outpatient clinic for evaluation of shortness of breath and fatigue. He had been diagnosed with HCL-C 8 years previously. The diagnosis was based on splenomegaly, absence of peripheral lymphadenopathy, pancytopenia, and a bone marrow aspirate and core biopsy that contained patchy interstitial infiltrates of enlarged lymphocytes with low nuclear-cytoplasmic ratios, reticular chromatin, and cytoplasmic projections (D. Variakojis, MD, written communication, July 1989). Furthermore, the bone marrow was technically difficult to aspirate. He did not respond to treatment with interferon alfa (u.-IFN), but achieved long-term remission following treatment with deoxycoformycin (Pentostatin). The patient had relapsed 1 year prior to the current presentation and was treated with 2-clorodeoxyadenosine. He had no palpable splenomegaly or lymphadenopathy at the latest presentation. Chest radiography showed pulmonary infiltrates consistent with pneumonia. A complete blood count showed moderate leukopenia, anemia, and a normal platelet count. To confirm a suspected second relapse, a bone marrow aspirate and core biopsy were performed.

PATHOLOGIC FINDINGS

Hematopathology

As in the first relapse, the bone marrow aspirate and care biopsy showed occasional enlarged lymphocytes with low nuclear-cytoplasmic ratios; eccentric, round to oval nuclei; reticular chromatin; indistinct nucleoli; and pale cytoplasm with easily demonstrable projections (Figure 1, A). Some abnormal lymphocytes had indented nuclei or prominent nucleoli. Binucleated lymphocytes were not seen. Many abnormal lymphocytes had strong tartrate-resistant acid phosphatase (TRAP) activity (Figure 1, B).

Flow Cytometry

Immunophenotyping of heparinized marrow by flow cytometry performed 1 hour after collection showed cells with slightly greater forward and right-angle light scatter than that of normal lymphocytes. These abnormal cells were CD19+ (Figure 2), CD20+, CD22+, FMC7+, CD23-, CD5- (all antibodies supplied by Immunotech, Miami, Fla), and sIgGkappa-restricted (Dako Corporation, Carpinteria, Calif), consistent with a mature B-cell monoclonal population. In addition, this population was bright CDllc+ (Dako) (Figure 2, A), CD25+ (Becton Dickinson, San Jose, Calif) (Figure 2, B), dim CD10+ (Immunotech) (Figure 2, C), and did not express CD103 (2G5, Immunotech SA) (Figure 2, D). Absence of CD103 was confirmed on repeat analysis the same day with adequate positive control and by analyzing cryopreserved material with a different anti-- CD103 antibody (Ber-Act8, Dako; data not shown). The patients pneumonia resolved following antibiotic therapy. He responded well to a second cycle of 2-chlorodeoxyadenosine and is still alive 9 years after initial presentation.

COMMENT

The differential diagnosis of rare indolent mature B-cell neoplasms with cytoplasmic projections in older adults with splenomegaly includes SLVL and HCL.3-5 Although the classification of HCL has been questioned,3 3 variants of HCL have been described6: HCL-C, variant HCL (HCL-- V,7,8 type II HCL2), and Japanese variant HCL (HCL-J2,9). It is important to accurately diagnose these entities, as they have different clinical and biologic features, particularly regarding the response to alpha-IFN.2,6

Splenic lymphoma with villous lymphocytes was previously called "lymphoma simulating hairy cell leukemia" and "lymphoplasmacytic lymphoma with circulating villous lymphocytes" and was more precisely defined in 1987.10 Splenic lymphoma with villous lymphocytes is associated with a female predilection, mean age at onset of 68 years, leukocytosis, TRAP inactivity, successful marrow aspirates, and a good response to splenectomy.10 The relationship between SLVL and splenic marginal zone lymphoma, another low-grade B-cell neoplasm, is controversial.11 The pathologic features of SLVL partially overlap those of splenic marginal zone lymphoma,12 and some authors have stated that SLVL and splenic marginal zone lymphoma are histologically indistinguishable.13 The diagnostic criteria for splenic marginal zone lymphoma are undergoing reevaluation 14 and are discussed elsewhere.11-14

Classic HCL was first described in 1958 and was called "leukemic reticuloendotheliosis."15 Classic HCL is associated with a striking white male predilection,10,15 a mean age at onset of 50 years,10 pancytopenia,10,15 infections,6,10,15 unsuccessful marrow aspirates,6 strong TRAP activity, and good response to alpha-IFN or purine analogues.6 Variant HCL is a variant first described in 19807 and is associated with predilection for neither sex, older mean age at onset (70 years), leukocytosis, absence of infection, successful marrow aspirates, TRAP inactivity, and poor response to alpha-IFN.1,7,8 Classic HCL and HCL-V are rare in Japan.2 Japanese variant HCL is a recently described variant9 that has occurred exclusively in Japan.2 To our knowledge, the specific environmental or genetic factors that might be responsible for this geographic distribution have not been reported. Japanese variant HCL shares some features with HCL-V in that it also is associated with predilection for neither sex, older mean age at onset (60 years), leukocytosis, successful marrow aspirates, absent to weak TRAP activity, and poor response to alpha-IFN.2,9 Further studies are necessary to determine whether HCL-J or HCL-V are true variants of HCL or whether they are distinct entities separate from HCL.

Although SLVL, HCL-C, HCL-V, and HCL-J are morphologically similar, histologic and ultrastructural differences exist. Cytoplasmic projections are easily demonstrable in SLVL, HCL-C, and HCL-V, but not in HCL-J.8,9,16 Cells of SLVL are smaller than HCL-C cells, have higher nuclear-cytoplasmic ratios,10 more condensed chromatin,4 demonstrable nucleoli in 50% of cases, and may be spindled.10 Cells of HCL-C have low nuclear-cytoplasmic ratios17; central or eccentric,17 oval, indented, or occasionally bilobed nuclei; reticular ("lacy") chromatin; indistinct nucleoli; and ribosome-lamella complexes.16 Compared to HCL-C cells, HCL-V cells are smaller and have higher nuclear-cytoplasmic ratios; central,10,17 rounded, or indented2 hyperchromatic nuclei; a prominent nucleolus; intensely basophilic cytoplasm; and no ribosome-lamella complexes.11,10 Binucleated HCL-V cells are common.8 Cells of HCL-J have round hyperchromatic nuclei, inconspicuous nucleoli? and rarely contain ribosome-lamella complexes.9 In addition, HCL-C, HCL-V, and HCL-J preferentially infiltrate splenic red pulp,2,8,18 whereas SLVL preferentially infiltrates splenic white pulp.2 Also, paraprotein in the serum (as indicated by a monoclonal band) is common in SLVL,2,8 rare in HCL-Clb and HCL-VII and absent in HCL-J.2

Flow cytometry is invaluable in the differential diagnosis of "hairy" lymphocytes because SLVL, HCL-C, HCL-V, and HCL-J often have different immunoprofiles. All 4 entities resemble mature B cells in that they consistently express CD19, CD20, CD22, and FMC7 and do not express CD5.4,18,19 However, they may differ in their expression of CD10, CD11c, CD23, CD24, CD25, CD103, and HCL-associated antigen (HC2), an activation antigen defined by a monoclonal antibody raised against lymphocytes of HCL.20 Splenic lymphoma with villous lymphocytes is typically CD24+, CD25-, sIgM+, K-restricted more often than X-restricted, CD103-, HC2-, and variably expresses CD23, CD10, or CDllc.4,8 Classic HCL has forward and right-angle light scatter slightly greater than that of normal lymphocytes5 and is typically CD10-, CD23-, CD25+, sIgM+, K-restricted equally often as X-restricted, bright CDllc+, CD103+, HC2+, and variably expresses CD24.4,5,8,19 Variant HCL is typically CD10-, CD23-, CD24-, CD25-, sIgGI, K-restricted less often than ,-restricted, HC2-, dim CD1 JC+18, and variably expresses CD103.4,8 Limited available data show HCL-J to be CD10-, CD24-, CD25-, sIg- or weakly sIgGkappa+, bright CDllc+, and variably expressive for CD103.2,18 Key features of HCL-C, HCL-V, HCL-J, and our case are summarized in the Table.

Our case does not fit neatly into existing diagnostic categories. Poor response to alpha-IFN and absence of CD103 reactivity raise the possibility of SLVL. However, pancytopenia, reticular chromatin, abundant cytoplasm, expression of CD25, and very intense expression of CD11c strongly argue against SLVL. Furthermore, SLVL is almost always TRAP inactive.21

Our case was unusual because it clinically, morphologically, and cytochemically resembled HCL-C but did not have the immunoprofile of HCL-C, HCL-V, or HCL-J regarding CD10, CD25, and CD103. Expression of CD10 and CD25 makes HCL-V or HCL-J extremely unlikely. Although data are limited, HCL-V is CD10+ in only about 20% of cases,4,8 whereas all 11 cases of HCL-J studied by Yamaguchi et al were CD10-.18 To our knowledge, all cases of HCL-V and HCL-J with available immunophenotype have been CD25-.1,2,4,8,18 In addition, white race and intense TRAP activity strongly argue against HCL-J.

The case is also atypical for HCL-C, as it was CD10+ and CD103-. Expression of CD10 in HCL-C has been reported in only 50/64 to 26%19 of cases. It is exceedingly rare for HCL-C not to express CD103. CD103 reacts with several monoclonal antibodies that identify the same HCL-- associated molecule.2 Expression of CD103 in HCL-C has been reported in 98%4 to 100%8,19,23,24 of cases. On the other hand, Sainati et all and Machii et ale demonstrated CD103 positivity in only 40% and 30% of cases of HCL-V and HCL-J, respectively. Details of CD103- cases were not provided, so it is difficult to draw conclusions as to the clinical significance of CD103 negativity, although our patient responded poorly to alpha-IFN.

We entertained the possibility that CD103 negativity in our case might indicate a falsely negative result, a loss of previous CD103 positivity, or an incorrect original diagnosis. Since the specimen demonstrated excellent viability, was processed promptly, and had an adequate positive control, it is unlikely that CD103 negativity was due to degeneration or suboptimal processing. Of note, CD103 has been stable in vitro24,25 and in cryopreserved marrow (C.L.G., unpublished data, 1997). Furthermore, we demonstrated negativity to 2 anti-CD103 antibodies. This argues against selective deletion of tested epitopes and suggests that CD103 was entirely absent.

The original diagnosis of HCL was made based on fulfillment of many classic clinical and morphologic criteria26; however, since the diagnosis was made without flow cytometry, we cannot exclude phenotypic changes related to therapy or time, although CD103 has been stable following treatment with alpha-IFN or deoxycoformycin.27

In summary, we presented a case of HCL with an immunoprofile different from that of HCL-C, HCL-V, and HCL-J in that the cells were CD10+, CD25+, and CD103-. We also reviewed the clinical, morphologic, cytochemical, and immunophenotypic criteria helpful in differentiating HCL and SLVL. This case emphasizes the variability of hairy B-cell neoplasms and the need to correlate all clinical and pathologic data in reaching a diagnosis.

We thank the technologists of the flow cytometry laboratory at Northwestern University Medical School for their assistance with the case, and Vanessa A. Jones, MT, for her assistance with the figures.

References

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Accepted for publication April 24, 2000.

From the Departments of Pathology (Drs Wu and Goolsby) and Internal Medicine (Dr Kwaan), Northwestern University Medical School, Chicago, Ill.

Reprints: Mark Li-cheng Wu, MD, Department of Pathology & Laboratory Medicine, UCLA Medical Center, Center for the Health Sciences, Room A2-179, Box 951732, Los Angeles, CA 90095-1732.

Copyright College of American Pathologists Nov 2000
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