Fluorescence in situ hybridization: method of choice for a definitive diagnosis of mantle cell lymphoma

A practical guide to laboratory investigations at diagnosis and follow up in Waldenström macroglobulinaemia: recommendations from the Medical and Scientific Advisory Group, Myeloma Australia, the Pathology Sub-committee of the Lymphoma and Related Diseases Registry and the Australasian Association of Clinical Biochemists Monoclonal Gammopathy Working Group

Waldenström macroglobulinaemia (WM) is an indolent non-Hodgkin lymphoma which usually presents with symptoms related to infiltration of bone marrow or other tissues like lymph nodes, liver or spleen and has certain unusual clinical manifestations, e.g., renal and central nervous system (CNS) involvement. It also has an array of laboratory features including hypersecretion of IgM, cryoglobulinaemia, increased plasma viscosity and identification of mutated MYD88^L265P in more than 90% of cases. In this review, we aim to provide a guide to the laboratory investigations recommended for WM at initial diagnosis and at follow-up. A discussion on the nuances of diagnosis and differential diagnoses is followed by bone marrow (BM) assessment, measurement of paraprotein and other ancillary investigations. Recommendations are provided on laboratory work-up at diagnosis, in the asymptomatic follow-up phase, and during and post-treatment. Finally, we briefly discuss the implications of laboratory diagnosis in regard to recruitment and monitoring on clinical trials.

Biomarkers in Hematological Malignancies: A Review of Molecular Testing in Hematopathology

BACKGROUND

Molecular interrogation of genetic information has transformed our understanding of disease and is now routinely integrated into the workup and monitoring of hematological malignancies. In this article, a brief but comprehensive review is presented of state-of-the-art testing in hematological disease.

METHODS

The primary medical literature and standard textbooks in the field were queried and reviewed to assess current practices and trends for molecular testing in hematopathology by disease.

RESULTS

Pertinent materials were summarized under appropriate disease categories.

CONCLUSION

Molecular testing is well entrenched in the diagnostic and therapeutic pathways for hematological malignancies, with rapid growth and insights emerging following the integration of next-generation sequencing into the clinical workflow.

Amplification of IGH/CCND1 fusion gene in a primary plasma cell leukemia case

The IGH/CCND1 fusion gene has been reported in many hematologic tumors such as mantle cell lymphoma, chronic lymphocytic leukemia, prolymphocytic leukemia, multiple myeloma, and plasma cell leukemia. We report a case of plasma cell leukemia showing five IGH/CCND1 fusion signals by interphase fluorescence in situ hybridization (FISH). Conventional cytogenetic analysis and multicolor spectral karyotyping showed a complex karyotype that did not include t(11;14). Metaphase FISH studies revealed three IGH/CCND1 fusion signals, two of which were amplified signals. These findings indicate that IGH/CCND1 fusion gene was amplified and interspersed in several chromosomes. The patient was treated with intensive chemotherapy. However, the clinical course was very aggressive. The amplification of the IGH/CCND1 fusion gene may contribute to the aggressive course of the disease. To our knowledge, this is the first case showing amplification of the IGH/CCND1 gene in plasma cell neoplasms.

Magnetic resonance imaging with pathological correlation in a case of mantle cell lymphoma of the parotid gland: a case report

Introduction

Mantle cell lymphoma is a rare non-Hodgkin's lymphoma. It is a subtype of B-cell lymphoma with frequent involvement of the bone marrow and the gastrointestinal tract. Isolated parotid gland involvement seldom occurs. Here we report an unusual case of isolated infiltration of the parotid gland by mantle cell lymphoma. The aim of our study is to correlate magnetic resonance imaging findings with the histological features of the disease. To the best of our knowledge, no similar radiological findings of mantle cell lymphoma have been published before.

Case presentation

A 72-year-old Caucasian woman presented with a painful left parotid enlargement. She was diagnosed with mantle cell lymphoma involving the left submandibular gland seven years prior to presentation. Her whole body CT scan showed the absence of pathologically enlarged lymph nodes. However, a magnetic resonance imaging showed enlargement of her left parotid gland and an abnormal parenchyma with mixed-type solid and cystic lesions. A biopsy of her left parotid gland and subsequent histological examination confirmed a mantle cell lymphoma (common variant) relapse.

Conclusion

Although rare, the involvement of parotid gland with mantle cell lymphoma must be considered in the differential diagnosis of parotid tumors.

The cut-off levels of CD23 expression in the differential diagnosis of MCL and CLL

Flow cytometric analysis of CD23 expression in CD5-positive B-cells is a widely applied method in the differential diagnosis of chronic lymphocytic leukaemia (CLL) and mantle cell lymphoma (MCL). According to the most accepted criteria, the leukaemic cell population is CD19/CD5/CD23 triple positive in CLL but CD23-negative in MCL. Recently, several groups have reported CD23-positive MCL cases; however, these studies mostly analysed only CD23 positivity but not intensity. To determine the role and the cut-off levels of CD23 positivity and intensity in the differential diagnosis of CLL and MCL, 26 cases of MCL and 84 cases of CLL were compared using flow cytometric analysis. Our results suggest that high values of CD23 positivity (>92.5%) and/or high fluorescence intensity (>44.5 mean fluorescence intensity (MFI)) of CD23 are related to CLL, whereas low CD23 positivity (<30%) is related to MCL. However, cases with intermediate CD23 positivity (between 30 and 92.5%) and lower intensity (<44.5 MFI) can either belong to CLL or MCL. In these cases, additional tests such as FISH analysis of the translocation t(11;14) or immunohistochemical detection of cyclin D1 overexpression are required to differentiate CLL from MCL.

Automated FISH analysis using dual-fusion and break-apart probes on paraffin-embedded tissue sections

Detecting balanced translocations using tissue sections plays an important diagnostic role in cases of hematological malignancies. Manual scoring is often problematic due to truncation and overlapping of nuclei. Reports have described automated analysis using primarily tile sampling. The aim of this study was to investigate an automated fluorescent in situ hybridization analysis method using grid sampling on tissue sections, and compare the performance of dual-fusion (DF) and break-apart (BA) probes in this setting. Ten follicular, 10 mantle cell lymphoma, and 10 translocation-negative samples were used to set the threshold of false positivity using IGH/CCND1, IGH/BCL-2 DF, and IGH BA probes. The cut-off distances of red and green signals to define fusion signals were 0.5, 1.0, and 1.2 mum for the IGH/CCND1, IGH/BCL-2 DF, and IGH BA probes, respectively. The mean false positivity of grid units was 5.3, 11.4, and 28.1%, respectively. Ten to 14 additional samples analyzed blindly and were correctly classified using each probe. Discriminating positive and negative samples using automated analysis and grid sampling was possible with each probe, although different definitions of fusion signals were required due to the different physical distances between the DNA probes. Using the DF probes resulted in lower false positivity, which was less affected by signal numbers per grid units.

Application of Immunohistochemistry in the Diagnosis of Non-Hodgkin and Hodgkin Lymphoma

Context.—Beginning with the immunologic classifications of Lukes and Collins and Kiel and culminating in the Revised European-American Lymphoma and World Health Organization classifications, the diagnosis of lymphoid tumors relies heavily on the determination of cell lineage, maturation, and function, based on antigen expression in addition to morphology and clinical features. Technologic advances in immunology, antibody production, genetic analysis, cloning, and the identification of new genes and proteins by microarray and proteomics have provided pathologists with many antibodies to use in routine diagnosis.

Objective.—To provide guidance to the practicing pathologist in the appropriate selection of an antibody panel for the diagnosis of lymphoma based on morphology and relevant clinical data and to avoid pitfalls in the interpretation of immunohistochemical data. Attention is given to some of the newer antibodies, particularly against transcription factors, that are diagnostically and prognostically useful.

Data Sources.—The information presented in this article is based on review of the literature using the OVID database (Ovid MEDLINE 1950 to present with daily update) and 20 years of experience in diagnostic hematopathology.

Conclusions.—Immunophenotyping is required for the diagnosis and classification of lymphoid malignancies. Many paraffin-reactive antibodies are available to the pathologist but most are not specific. To avoid diagnostic pitfalls, interpretation of marker studies must be based on a panel and knowledge of a particular antigen's expression in normal, reactive, and neoplastic conditions.

CD5-positive mucosa-associated lymphoid tissue (MALT) lymphoma of ocular adnexal origin: usefulness of fluorescence in situ hybridization for distinction between mantle cell lymphoma and MALT lymphoma

Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue type (MALT lymphoma) usually lacks CD5 expression. Herein is described two cases of CD5-positive MALT lymphoma of ocular adnexal origin. The differential diagnosis between CD5-positive MALT lymphoma and mantle cell lymphoma (MCL), notably cyclin D1-negative MCL, was difficult because both cases consisted histologically of small to medium-sized cells with diffuse or vaguely nodular growth pattern, and the neoplastic cells were positive for CD5 and negative for cyclin D1. Somatic mutation analysis of the immunoglobulin heavy chain variable region (VH) gene in case 1 found a relatively higher mutation frequency (5.0%), which was not definitive to rule out MCL. Interphase fluorescence in situ hybridization (FISH) on paraffin-embedded section using IgH/cyclin D1 (CCND1) probe showed that in both cases there was no molecular evidence of t(11;14), finally leading to the diagnosis of CD5-positive MALT lymphoma. Although the present two patients had no recurrence over 34 months after initial diagnosis, careful observation is needed because the clinicopathological significance of MALT lymphoma with this rare phenotype remains obscure.

Mammalian Target of Rapamycin Inhibitors as Possible Adjuvant Therapy for Microscopic Residual Disease in Head and Neck Squamous Cell Cancer

Molecular therapeutics identifies an aberration in tumors to select patients that benefit from molecular targeted therapy. Overexpression of eIF4E in histologically "tumor-free" surgical margins of head and neck squamous cell cancer (HNSCC) patients is an independent predictor of recurrence and is functionally activated through the Akt/mammalian target of rapamycin (mTOR) pathway. Although mTOR inhibitors are cytostatic agents, best used in combination therapy, we hypothesize that they can be used as long-term single agents in an HNSCC model of minimal residual disease (MRD). CCI-779, an mTOR inhibitor, arrested growth of a phosphatase and tensin homologue deleted on chromosome 10 (PTEN) abnormal HNSCC cell line FaDu, inhibiting phosphorylation of 4E-binding protein 1, resulting in increased association with eIF4E and inhibition of basic fibroblast growth factor and vascular endothelial growth factor. Fluorescence in situ hybridization detected PTEN abnormalities in 68% of patient tumors and 35% of tumor-free margins. CCI-779 inhibited growth of established tumors in nude mice. However, in the MRD model, there were significant differences in the tumor-free rate between the control (4%) and the treatment group (50%), and the median tumor-free time was 7 versus 18 days, respectively (P < 0.0001). In those animals that formed tumors, CCI-779 caused a significant decrease in the tumor volume. The Kaplan-Meier curve showed that CCI-779 significantly increased survival (P < 0.0001). The mTOR pathway was inhibited in peripheral blood mononuclear cells potential surrogate markers of response to therapy. Stable transfection of FaDu with luciferase allowed us to monitor the effects of CCI-779 with bioluminescence imaging in the MRD model. These results pave the way for a clinical trial using targeted molecular therapy with CCI-779 as a single agent for mTOR-activated residual cells.

The specificity of interphase FISH translocation probes in formalin fixed paraffin embedded tissue sections is readily assessed using automated staining and scoring of tissue microarrays constructed from murine xenografts

Implementation of interphase fluorescence in situ hybridization (FISH) assays in the clinical laboratory requires validation against established methods. Validation tools in common use include exchange of consecutive sections with another institution that has already established the FISH assay, comparison with conventional banded metaphase cytogenetics, confirmation of specificity using probed normal metaphases, consecutive paraffin sections of a validation set tested by a reference laboratory, and specificity assessment against well characterized cell lines. We have investigated the feasibility of using tissue microarrays (TMA) constructed from murine xenografts as a preliminary specificity-screening tool for validation of interphase FISH assays. Cell lines currently in use for FISH controls are used to generate xenografts in SCID mice which are fixed in formalin and paraffin embedded. A TMA is constructed using duplicate donor cores from the xenograft blocks. Xenografts used represent a wide range of translocations used routinely for formalin fixed paraffin embedded sections evaluated by FISH. Probe cocktails (Abbott-Vysis), for several non-random translocations associated with hematologic neoplasms and soft tissue sarcomas have been used in this manner. On-line deparaffinization, cell conditioning, and prehybridization steps are automated using a staining workstation (Ventana Discovery XT); hybridization and stringency washes are performed manually offline. FISH-probed TMAs are tracked using a Metasystems image scanner and analyzed using classifiers specifically developed for each molecular abnormality. FISH results for each xenograft in the TMA correspond exactly to the genotype previously established for the parent cell line from which the xenograft was prepared. Moderate complexity tissue microarrays constructed from murine xenografts are excellent validation tools for initial assessment of interphase FISH probe specificity.

Cyclin D1 protein overexpression and CCND1 amplification in breast carcinomas: an immunohistochemical and chromogenic in situ hybridisation analysis

Conflicting results on the prevalence of cyclin D1 ovexpression and its correlation with CCND1 amplification and outcome of breast cancer patients have been reported. Owing to limited sensitivity and specificity of most antibodies against cyclin D1, evaluation of cyclin D1 immunoexpression is reported to be problematic. The aims of this study were to assess the prevalence of cyclin D1 expression in breast carcinomas using the SP4 rabbit monoclonal antibody; to correlate cyclin D1 expression with amplification, assessed using chromogenic in situ hybridisation (CISH); and to analyse the relationship between CCND1 amplification and overexpression with clinicopathological parameters and outcome in a tissue microarray containing replicate tumour samples from 245 breast cancer patients. Immunohistochemistry for cyclin D1 was performed using the SP4 and the results were scored according to the Allred scoring system. CISH was carried out using the Zymed CCND1 SpotLight probe. CISH signals were counted in 60 morphologically unequivocal neoplastic cells. Amplification was defined as >5 signals per nucleus in more than 50% of cancer cells, or when large gene copy clusters were seen. Strong cyclin D1 expression and CCND1 amplification were found in 67.4 and 14.5% of the cases, respectively. A strong correlation between cyclin D1 overexpression and CCND1 amplification was demonstrated (P<0.0001). Cyclin D1 expression showed a positive correlation with hormone receptor expression (both ER and PgR, P<0.0001). An inverse correlation was observed between an immunohistochemical panel of 'basal-like' markers and both cyclin D1 overexpression (P<0.0001) and CCND1 amplification (P<0.0001). On univariate analysis cyclin D1 expression showed a correlation with longer overall survival (OS). Neither cyclin D1 nor CCND1 were independent prognostic factors for disease-free survival or OS. The results of this study confirm the association between cyclin D1 overexpression and positivity for hormone receptors and the lack of CCND1 amplification in basal-like breast carcinomas.

Tumor Cell Nuclei Extraction From Paraffin-Embedded Lymphoid Tissue for Fluorescence In Situ Hybridization

In this study the authors evaluated a technique for isolating intact tumor nuclei from paraffin-embedded lymphoma samples before performing FISH testing to detect the lymphoma-specific trans-location t(11;14) that defines mantle cell lymphoma. Well-characterized surgical pathology cases of mantle cell lymphoma were identified from pathology archives. Thin sections were cut from the paraffin-embedded tissue blocks. One section was stained using hematoxylin and eosin and an area composed exclusively of malignant cells was identified and marked on the slide. The corresponding area of the tissue block corresponding to this region underwent needle core biopsy, and the tissue was processed to isolate tumor cell nuclei and deposited onto a glass slide. The paired sample preparations underwent routine FISH testing for detection of the t(11;14)(q13;q32) chromosomal trans-location. DNA probe hybridization quality was compared between the tissue and isolated nuclei. Individual tumor cell nuclei were successfully extracted from each of the tissue blocks. The t(11;14) trans-location was detected by FISH in all of the samples diagnosed as mantle cell lymphoma. The hybridization signals found in the nuclei of extracted tumor cells were bright, planar, and easily identified. Detection of signal was superior to that on whole tissue samples, where signals often overlapped or were truncated. This technique produces intact nuclei for analysis, preserves the tissue block for additional studies, and allows sampling of a specific area of the tissue block. This approach may be particularly useful when the amount of diagnostic tissue is limited.

Cytogenetics of lymphomas

Cytogenetic analysis is now a routine part of the diagnosis and management of a significant number of lymphoid malignancies. Whilst conventional cytogenetics remains the most comprehensive method for assessing chromosome abnormalities, the technical difficulties associated with conventional cytogenetics in most lymphomas has resulted in increased use of fluorescence in situ hybridisation (FISH) to identify specific abnormalities that are useful in either the diagnosis or management of these disorders. The finding of one of the Burkitt's translocations is of major importance in the diagnosis of Burkitt's and Burkitt's-like lymphomas, whereas the t(14;18), although seen in most follicular lymphomas (FL), is not usually required to make a diagnosis. Thus, whilst cytogenetics may be of interest in FL, it is not an essential part of the diagnostic work-up. Conventional cytogenetics may be useful for identifying markers of resistance to Helicobacter pylori therapy in MALT lymphomas. In disorders such as Hodgkin lymphoma, hairy cell leukaemia and lymphoplasmacytoid lymphoma, although many cytogenetic abnormalities have been observed, no consistent or specific abnormalities have been identified and so, at this point in our knowledge of the genetics of these disorders, cytogenetics cannot be considered a useful test for either diagnosis or prognosis. In contrast, the diagnosis of mantle cell lymphoma is now dependent upon the identification of the 11;14 translocation that results in cyclin D1 up-regulation. It is widely acknowledged that FISH is the most consistently useful test to identify the juxtaposition of the CCND1 and IGH genes in mantle cell lymphoma and is regarded as the 'gold standard'. FISH also has a role in identifying genetic abnormalities of prognostic significance in chronic lymphocytic leukaemia. Given the wealth of genetic and cytogenetic abnormalities that are continuing to be found in chronic lymphoid malignancies, it will be some time before the optimal use of both conventional cytogenetics and FISH is established in the diagnosis and management of lymphomas.

SP4, a Novel Anti-Cyclin D1 Rabbit Monoclonal Antibody, Is a Highly Sensitive Probe for Identifying Mantle Cell Lymphomas Bearing the t(11;14)(q13;q32) Translocation

Immunohistochemistry is the most widely used approach in the diagnosis of mantle cell lymphoma (MCL). However, its reliability may be hampered by several technical reasons, necessitating the use of alternative techniques such as the identification of the t(11;14)(q13;q32) translocation to characterize such lesions. The authors compared two monoclonal antibodies (DCS-6 and SP4) for assessing cyclin D1 immunoreactivity in a series of 22 MCLs. Their results documented that SP4, a novel rabbit monoclonal antibody, is more effective than the mouse monoclonal antibody DCS-6, one of the most commonly used reagents in daily practice. Although DCS-6 and SP4 were capable of identifying cyclin D1 immunoreactivity in 95.4% and 100% of the cases analyzed, respectively, the prevalence of cyclin D1 immunoreactive neoplastic cells was significantly (P < 0.0001) higher with SP4 (86.6 +/- 13.1%) than with DCS-6 (39.8 +/- 32%). Moreover, the staining intensity was faint in 16 (76.2%) cases and moderate to strong in 5 (23.8%) cases immunostained with DCS- 6, while all the cases showed a moderate to strong immunoreactivity with SP4 (P < 0.0001). According to an arbitrary score based on the percentage of immunoreactive neoplastic cells and staining intensity, only 10 (45.4%) cases were considered high cyclin D1 expressors after staining with DCS-6, whereas all the cases were high expressors with SP4 (P < 0.0001). These data provide evidence that the SP4 monoclonal antibody may be a fast, easy-to-interpret, and reliable surrogate for the detection of the (11;14) translocation by molecular techniques.

Lymphoma associated chromosomal abnormalities can easily be detected by FISH on tissue imprints. An underused diagnostic alternative

BACKGROUND

Fluorescence in situ hybridisation (FISH) is useful for detecting specific chromosomal abnormalities in various tumours. In lymphomas, diagnosis is frequently made using paraffin wax embedded tissue. However, FISH performed under these conditions presents potential technical problems and difficulties in interpretation.

AIMS

To show that FISH using tissue imprints and cytopreps or alternatively, bone marrow (BM) smears, constitutes an easy and rapid strategy to overcome these constraints.

METHODS

The study comprised 46 patients with lymphoma. Sixty nine tissue imprints, cytopreps, or BM smears were analysed by FISH. Dual colour, dual fusion FISH probes were used to detect the t(8;14), t(11;14), and t(14;18) translocations, whereas a dual colour breakapart FISH probe was used to detect chromosomal translocations involving the BCL6 gene.

RESULTS

Tissue imprints and cytopreps were successfully hybridised in all 52 cases, whereas hybridisation was successful in 16 of 17 archival BM smears. All patients could be analysed to identify either the presence or absence of chromosomal translocations.

CONCLUSIONS

The use of tissue imprints, cytopreps, or BM smears to identify chromosomal abnormalities by FISH is a rapid and useful ancillary approach for diagnostic purposes. Therefore, it could be used on a routine basis whenever fresh samples are available.

Best Practice No 185. Cytological and molecular diagnosis of lymphoma

With the advances in molecular pathology, the cell as a morphological and functional unit has become essential in the diagnosis of lymphoma. Conventional staining, preparation, and interpretation of cells, as seen in fine needle aspiration cytology (FNAC), often used as a first line investigation of lymphadenopathy, is being supplemented with an array of immunocytochemical and molecular analyses, aimed not only at a more precise disease definition, but also at recognising factors that can predict prognosis and response to treatment. Accepting the pitfalls of conventional cytomorphology, this review looks at molecular changes characteristic to particular lymphomas and explores the currently available technology for their detection, with particular reference to cytological material. Future protocols for the diagnosis and management of patients with lymphadenopathy should include FNAC as an initial investigation, followed by immunocytochemistry and molecular investigations. Tissue biopsy, the conventional method of diagnosis, may be avoided in selected cases.

Mantle cell lymphoma

PURPOSE OF REVIEW

Mantle cell lymphoma is the B-cell lymphoma with the worst prognosis. Until now, no standard treatment has resulted in cure. Improvements in understanding of the disease are needed to advance therapeutic efforts.

RECENT FINDINGS

Pathology and immunohistochemistry can identify the subset of patients with the worse prognosis. New data suggest that at least a subset of mantle cell lymphoma cases have undergone some form of antigene selection, and particular types of Ig gene rearrangement seem to give a better prognosis. The cell cycle, the ATM, gene and the nuclear factor kappaB pathways are the main targets of the genetic abnormalities occurring in mantle cell lymphoma: new genomic and expression data have been recently published. Unfortunately, this progress has not yet brought any major improvements in therapeutic approaches, which still remain highly unsatisfactory. Autologous and allogenic bone marrow transplantations appear to be the only current treatments that might improve the outcome of patients with PMCL. New additional treatment modalities are currently under investigation.

SUMMARY

This review summarizes all the most recent data published on the biology and treatment of mantle cell lymphoma.

Paraffin section interphase fluorescence in situ hybridization in the diagnosis and classification of non-hodgkin lymphomas

Cytogenetic data can contribute valuable information that may assist in the diagnosis and classification of non-Hodgkin lymphomas and may in some cases also provide prognostic information. Interphase fluorescence in situ hybridization (FISH) studies offer the ability to assess for characteristic cytogenetic abnormalities even when material for standard metaphase cytogenetic analysis is not available. This review discusses the use of FISH in paraffin-embedded material with particular attention paid to the use of intact thin paraffin sections. The basic principles of FISH analysis are summarized, the advantages and disadvantages of analysis of thin paraffin sections rather than intact nuclei are discussed, and the more commonly encountered artifacts are considered. Each of the well-characterized cytogenetic abnormalities that are associated with particular types of non-Hodgkin lymphoma and can be detected with commercially available FISH probes is discussed individually. In particular, their incidence in various types of lymphoma is reviewed, the types of commercially available FISH probes to detect such abnormalities are discussed, and clinical situations where such analysis can be of diagnostic utility are described.

Consistent immunostaining for cyclin D1 can be achieved on a routine basis using a newly available rabbit monoclonal antibody

Rabbit monoclonal antibody (MAb), which has become available only recently, theoretically combines the advantage of the high affinity attributable to its rabbit origin and the high specificity due to its monoclonal nature. Since immunohistochemical demonstration of cyclin D1 is notoriously difficult, this study aims to assess whether a newly available rabbit MAb against cyclin D1 (SP4) can improve the consistency of immunostaining, especially for the diagnosis of mantle cell lymphoma (MCL). A total of 150 cases of lymphoproliferative lesions, including 30 cases of MCL, histologic mimickers of MCL, and various types of lymphomas and leukemias, were studied. Immunostaining was performed on formalin-fixed, paraffin-embedded tissue sections using a labeled streptavidin-biotin peroxidase system in an automated immunostainer. All cases of MCL expressed cyclin D1, with a higher median staining score (8 out of a maximum of 12) compared with mouse MAb DCS-6 (score 4). In addition, 2 of 15 cases of B-cell chronic lymphocytic leukemia (B-CLL), 3 of 12 cases of multiple myeloma, and 2 of 5 cases of hairy cell leukemia were also positive. Comparable staining results could also be achieved by an optimized manual staining protocol. This study thus confirms the superior performance of the rabbit MAb SP4, which should permit consistent immunostaining for cyclin D1 to be readily achieved. The value of cyclin D1 immunohistochemistry in the differential diagnosis of MCL from other low-grade B-cell lymphomas is also affirmed, but with the caveat that rare cases of B-CLL can also be cyclin D1 positive.