Malignant Lymphomas |
1 Radboud University Nijmegen Medical Centre, Department of Pathology, Nijmegen, The Netherlands
2 Copenhagen University Hospital Herlev, Department of Pathology, Herlev, Denmark
3 LRF Immunodiagnostics Unit, Nuffield Department of Clinical Laboratory Sciences, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom
4 Serviço de Anatomia Patológica, Instituto Português de Oncologia, Lisboa, Portugal
5 Cytogenetics Unit, Spanish National Cancer Centre, (CNIO), Madrid, Spain
6 Department of Human Pathology and Oncology, University of Siena, Siena, Italy
7 Department of Pathology, University of Wuerzburg, Wuerzburg, Germany
8 APHP, Hôpital Henri Mondor, Département de Pathologie, Université Paris, Faculté de Médecine, Créteil, France
9 Hematopathology Department. Evaggelismos Hospital, Athens, Greece
10 Institute of Pathology, Aarhus University Hospital, Aarhus, Denmark
Correspondence: Anke van Rijk, Radboud University Nijmegen Medical Centre, Department of Pathology-824, P.O.Box 9101, 6500 HB Nijmegen, The Netherlands., E-mail: a.vanrijk{at}pathol.umcn.nl
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Design and Methods: Our study was initiated to determine the consistency between chromogenic in situ hybridization and fluorescence in situ hybridization, both using split-signal probes developed for the detection of chromosomal breaks. Five hundred and forty cases of 11 lymphoma entities and reactive, benign lymphoid tissues, collected from eight different pathology laboratories, placed on 15 fluorescence in situ hybridization pre-stained tissue microarray slides, were double stained for the chromogenic hybridization. For each core morphology and actual signal were compared to the original fluorescence hybridization results. In addition, hematoxylin background staining intensity and signal intensity of the double-staining chromogenic in situ hybridization procedure were analyzed.
Results: With respect to the presence or absence of chromosomal breaks, 97% concordance was found between the results of the two techniques. Hematoxylin background staining intensity and signal intensity were found to correspond. The overall morphology after double-staining chromogenic in situ hybridization had decreased compared to the initial morphology scored after split-signal fluorescence in situ hybridization staining.
Conclusions: We conclude that double-staining chromogenic in situ hybridization is equally reliable as fluorescence in situ hybridization in detecting chromosomal breaks in lymphoid tissue. Although differences in morphology, hematoxylin staining and chromogenic signal intensity vary between the tumor entities none of the entities appeared more easy or difficult to score.
Key words: double staining, CISH, split-signal, lymphoma diagnostics.
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Cytogenetic analysis, based on banding techniques, provides an overview of all cytogenetic aberrations. However, failed culturing of tumor cells, low mitotic indices and the lack of fresh material often complicate the use of this technology for routine diagnosis. Polymerase chain reaction (PCR)-based methods have the advantage of being sensitive and applicable in paraffin-embedded, formalin-fixed tissues, but only for those rare cases in which the chromosomal breaks involved in the translocation are clustered in a small area.6 In a recent review,7 it was nicely outlined that fluorescence in situ hybridization (FISH) has, over the last decade, become a firmly established technique and the method of choice in routine clinical practice.
To detect a translocation in a tumor cell one can use fusion probes [probes with different colors on different chromosomes (usually two)] which, in the case of a translocation, show a fusion signal.8 This procedure is feasible when complete cells or nuclei can be evaluated as in cytospins or preparations of isolated nuclei, but is more difficult in tissue sections, in which many nuclei are cut and/or overlap resulting in the presence of a complete signal in only a minority of cells, making interpretation cumbersome. In order to detect a chromosomal break reliably, it is desirable to be able to analyze tissue sections for translocations, since often only a minority of cells in a biopsy are lymphoma cells making a direct comparison with routine hematoxylin and eosin-stained tissue sections and immunostained slides important. Split-signal or break-apart probes use differently colored probes on both sides of a known breakpoint region, resulting in a fused signal in normal cells, and two different single colors when a chromosomal break occurs.9 This approach is advantageous in tissue sections since each single colored signal indicates a specific chromosomal break.
Just recently, the Euro-FISH project, representing a concerted multicenter retrospective study in the field of lymphoma diagnosis on paraffin-embedded material, demonstrated the robustness of a FISH protocol.10 In this study we describe double-staining chromogenic in situ hybridization (DuoCISH) as an alternative to split-signal FISH in the diagnosis of lymphoma.
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Table 1. Tissue microarrays used for DuoCISH that were previously split-signal FISH-stained during the Euro-FISH project.
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Probes and fluorescence and chromogenic in situ hybridization procedures
Eighteen months ago, four TMA were each stained with 16 different split-signal FISH probes The cut-off of the FISH probes is set at 85%, as determined by counting studies for CE-marking using FISH probes (unpublished data). Fifteen of these TMA (all FISH-stained with different probes) were subsequently DuoCISH-stained (Dako DuoCISH Kit, code no. SK108 and Dako Hematoxylin code S3301, Dako Denmark A/S, Produktionsvej 42, DK-2600 Glostrup, Denmark) and analyzed using bright field microscopy.
Four different TMA were used, each containing three samples of endemic Burkitts lymphoma, three anaplastic large cell lymphomas, three B-cell chronic lymphocytic leukemia/small lymphocytic lymphomas, four diffuse large B-cell lymphomas, three follicular lymphomas, three lymphoplasmacytic lymphoma, three gastric MALT lymphomas, three mantle cell lymphomas, three splenic marginal zone lymphomas, three sporadic Burkitts lymphoma, three T-lymphoblastic lymphomas and two reactive cases. The TMA were constructed using each tumor biopsy just once.
Slides were manually stained according to the manufacturers manual. A microwave step (Whirlpool JT356, 6th Sense Steam function, 10 min) was used instead of a water bath in the pretreatment procedure (FISH procedure). The hybridizer, 240V, CE-IVD S2451 was used for the pepsin digestion step, denaturation and hybridization step, red and blue chromogenic incubation steps and the counter stain step (FISH and CISH procedures). All previously split-signal FISH-stained slides had been stored in a dark room at 4°C (normal air pressure). One slide, stored unstained at 4°C, was freshly BCL6-stained using the FISH protocol previously described10 and subsequently DuoCISH-stained.
The following FISH probes (with chromosomal localization), serving as templates for DuoCISH-staining, were used: BCL10(1p22); IGK(2p11); ALK(2p23); BCL6(3q27); TCRG(7p14); TCRB(7q34); MYC(8q24); PAX5(9p13); CCND1(11q13); TCRAD(14q11); TCL1(14q32); IGH(14q32); MALT1(18q21); BCL2(18q21); BCL3(19q13); and IGL (22q11).
Data collection
The TMA signals were scored manually according to the manufacturers guidelines. A signal was considered co-localized (normal gene segment) if the red and blue signals (red and green for FISH) co-localized or if one red signal and one blue signal were separated by a distance equal to or less than two times the diameter of one signal or if two signals of the same size and color were separated by a distance equal to or less than two times the diameter of one signal. The signals were scored as a split signal (chromosomal break) if two signals of different color were separated by a distance more than two times the diameter of one signal (http://pri.dako.com/split-signal_flyer_interpreation_guide_20308.pdf). Tissue slides were analyzed by microscopic detection without the aid of software. Furthermore, data concerning morphology (good, intermediate, poor/failure), hematoxylin staining intensity (good, acceptable, weak, very weak, failure), signal intensity (strong, moderate, weak, very weak, absent/failure) and actual score (normal = PP, or abnormal = PPP/PB/PR/BR/PPR/PPB or any other combination except PP or no score; with P= purple, B=blue and R=red) were collected using a routine bright field microscope.
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After DuoCISH staining cores were analyzed by bright field microscopy and scored for morphology, hematoxylin staining intensity and signal intensity and signal (split or no split). Analysis of these slides was performed in a blinded fashion without prior knowledge of the original split-signal FISH scores or the diagnosis.
A total of 540 cores were DuoCISH stained of which 105 could not be scored; half of these were on three TMA (TMA n.2 stained with CCND1, 17 cases; TMA n. 2 stained with MALT, 19 cases and TMA n.3 stained with MYC, 15 cases). On the other hand, 11 cores that could not be scored in the Euro-FISH protocol were evaluable using CISH. Cores lost during the FISH protocol or lost during the DuoCISH procedure were not used for further analysis. Morphology, hematoxylin staining intensity, signal intensity and diagnostic result after CISH staining were analyzed per tumor entity. These data, except for diagnostic results, are shown in Figure 1. The number of cores of a specific entity with a specific score is represented as a percentage of the total number of cores of that entity. Although slight differences were seen for morphology (panel A), background staining (panel B) and signal intensity (panel C), overall there were no relevant differences between entities.
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Figure 1. Percentages per entity: (A) morphology, (B) background staining intensity and (C) signal intensity. The number of cores per entity with a specific score are shown as a percentage of the total number of cores analyzed for that specific entity.
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Figure 2. Mantle cell lymphoma tissue (1 core of a TMA with 36 cores) stained with (A) a CCDN1 split-signal probe during the Euro-FISH program (FITC- and Texas-Red labeled) and 1.5 year later (B) with the DuoCISH procedure (blue and red chromogen signals). (A) Leica microscope DM4000B, magnification 400x, colors corrected and clipping of the image after acquisition with Adobe Photoshop. (B) Zeiss Axioskop 2 plus microscope, magnification 400x, colors corrected and clipping of the image after acquisition with Adobe Photoshop.
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Table 2. Morphology of 540 cores that were scored during the Euro-FISH protocol (FISH) and 1.5 years later after CISH staining.
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While analyzing the hematoxylin counter-stain of the DuoCISH-stained slides it emerged that the intensity of this counter-stain is associated with the actual signal intensity (Table 3). We, therefore, combined these two datasets and showed that the intensity of the hematoxylin signal corresponds to the signal strength. From our data we conclude that strong hematoxylin and eosin background staining coincides with a strong signal; moderate staining with a moderate signal; weak staining with a weak signal and a failure of hematoxylin and eosin staining almost always results in a failure of signal intensity (highest percentages per intensity are given and shown in bold).
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Table 3. DuoCISH signal intensity compared to the intensity of the hematoxylin and eosin (H&E) background staining. Highest number of CISH signal intensity and corresponding background staining is given in bold. The percentage of the total number of screened cases is also calculated for these specific combinations.
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The results of this study show that the overall morphology weakened after prolonged storage of split-signal FISH-stained slides at 4°C. Although only one TMA with 36 cores was DuoCISH-stained directly following FISH, we feel that, from a morphological point of view, it is better to store the slides unstained. On the other hand if morphology scores of "good" and "intermediate" (which might be due to interpersonal variation in interpretation) were considered together, the morphology scoring was only 10% better during the Euro-FISH program.
It could, however, be argued that using old slides rather than fresh re-cuts from the TMA blocks unnecessarily complicated the study and that it decreased the number of usable cores. It should, however, be kept in mind that the availability of some tumor material is limited and, in some cases, can be precious to use just to validate a technique. We did, however, show that the freshly BCL6 FISH-stained TMA performed better after CISH than the previously FISH-stained slides. Nevertheless, we think that re-staining of "old" FISH-stained slides might, in certain cases (referral or second opinion), be desirable.
Additionally we showed that although differences in morphology, hematoxylin staining and CISH signal intensity varied between the tumor entities, none of the entities was easier or more difficult to score. During EuroFISH it appeared that endemic Burkitts lymphoma, anaplastic large cell lymphoma, lymphoplasmacytic lymphoma, splenic marginal zone lymphoma, T-lymphoblastic lymphoma and reactive lesions resulted in approximately 88% reliable scores and B-cell chronic lymphocytic leukemia/small lymphocytic lymphoma, diffuse large B-cell lymphoma, follicular lymphoma, mantle cell lymphoma and sporadic Burkitts lymphoma in 90% reliable scores, with the gastric MALT entity being the most difficult to score. Considering only the moderate and good CISH signal intensities, B-cell chronic lymphocytic leukemia/small lymphocytic lymphoma, reactive lesions, diffuse large B-cell lymphoma and lymphoplasmacytic lymphoma tumor samples had the best signal intensities (with B-cell chronic lymphocytic leukemia/small lymphocytic lymphoma giving the strongest and lymphoplasmacytic lymphoma the weakest signal) and anaplastic large cell lymphoma, follicular lymphoma, endemic Burkitts lymphoma and MALT lymphoma were the four weakest stained samples (with anaplastic large cell lymphoma the weakest and MALT the strongest). We, therefore, conclude that although FISH and CISH signals are generally comparable, a difficult-to-read split-signal FISH does not necessarily result in a weak CISH signal. Furthermore, it is very relevant that hematoxylin background staining intensity correlates with signal intensity, because it makes routine application of the procedure less dependent on staining variables.
In conclusion, we show, importantly for routine application, that split-signal DuoCISH is at least as reliable as split-signal FISH, a well-documented method for detecting chromosomal breaks in lymphoma samples. Since CISH can be performed in all pathology laboratories on routine samples, our findings suggest that this method could facilitate the classification of lymphomas.
AR was the principal investigator and takes primary responsibility for the paper. PC performed the laboratory work for this study and TSP designed the probes. SHD, JC, JCC, CCB, LL, AM, DM, EP and JH contributed the tissue blocks. AR performed the analysis and coordinated the research. AR and JK wrote the paper. None of the authors, except for TSP, who was directly employed by Dako A/S Denmark at the time of this study, reported potential conflicts of interest.
Received for publication May 19, 2009. Revision received July 31, 2009. Accepted for publication August 5, 2009.
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