Incidence of Diffuse Large B-Cell Lymphoma of Germinal Center B-Cell Origin in Whole Diffuse Large B-Cell Lymphoma: Tissue Fluorescence In Situ Hybridization Using t(14;18) Compared with Immunohistochemistry

Differences in the cytogenetic alteration profiles of diffuse large B-cell lymphoma among Chinese and American patients

To study the similarities and differences of cytogenetic alterations in diffuse large B-cell lymphoma (DLBCL) between Asian and Caucasian patients, we compared the cytogenetic profiles of Chinese and American DLBCL cases by analyzing conventional karyotypes and select fluorescence in situ hybridization (FISH) findings. We used interphase FISH analyses to determine the incidence of the t(14;18) and BCL6 and MYC rearrangements. Immunohistochemical analysis was used to categorize the lymphomas into the germinal center B-cell-like (GCB) or non-GCB-DLBCL subtypes, according to the Hans algorithm. Our data suggested that Chinese patients had cytogenetic profiles for GCB-DLBCL that differed from those of their American counterparts; specifically, the Chinese GCB patients exhibited greater frequencies of BCL6 rearrangements and gains of 1q and 11q but lower incidence of the t(14;18). Non-GCB-DLBCL in both the Chinese and American patients was characterized by recurrent gains of 3/3q and 18/18q. The incidences of both BCL6 rearrangement and t(14;18) were similar in Chinese and American non-GCB-DLBCL cases.

Clinical Impact of t(14;18) in Diffuse Large B-cell Lymphoma

OBJECTIVE

Recent studies have suggested that t(14;18) is present in a significant proportion of diffuse large B-cell lymphomas (DLBCLs). However, the prognostic significance of this translocation and its relationship with BCL-2 protein expression remains controversial. Our study aimed to investigate the predictive power of t(14;18) and BCL-2 protein expression in the prognosis of DLBCLs.

METHODS

Biopsy specimens from 106 DLBCLs were analyzed using interphase fluorescence in situ hybridization (FISH). Immunophenotypic analysis of CD20, CD3, CD10, BCL-6, MUM1 and BCL-2 was performed by immunohistochemistry. SPSS 13.0 software was used for statistical analysis.

RESULTS

The t(14;18) was identified in 27 of 106 cases (25.5%). The percentages of tumor cells expressing CD10, BCL-6, MUM1 and BCL-2 were 21.7%, 26.4%, 56.6% and 73.6%, respectively. The presence of this translocation was significantly correlated with the expression of CD10 and immunophenotypic subtype (p<0.001). No association was observed between BCL-2 protein expression and the presence of t(14;18). Multivariate analysis confirmed that both t(14;18) and BCL-2 expression were significantly associated with survival. Moreover, patients with t(14;18) had worse prognosis, compared with those with BCL-2 expression (for overall survival: hazard ratio, 4.235; 95%CI, 2.153-8.329, p<0.001 vs. hazard ration, 2.743; 95%CI, 1.262-5.962, p=0.011).

CONCLUSIONS

The t(14;18) is a useful prognostic tool for the evaluation of DLBCL immunophenotype and prognosis. The prognosis of GCB (germinal centre-like B cell) DLBCL patients should be made with the consideration of the presence of this translocation, and the detection of t(14;18) should be included as a routine diagnostic test in these cases.

Fluorescent in situ hybridization heating pretreatment: the key is temperature control

Fluorescent in situ hybridization (FISH) is a very useful tool for diagnostic and prognostic purposes in pathology. However, many laboratories still experience troubles when applying FISH to paraffin material. To overcome these difficulties, different pretreatments which include enzymatic digestion have been described. Usually, previous to digestion, a heating step is performed. The aim of this study was to compare the efficiency of the heating step with different buffers and different heating methods. We conclude that the main factor in the heating pretreatment is the temperature control, irrespective of the buffer used. Best results are obtained with any buffer by heating the slides to 99°C for 15 min followed by 10 min at room temperature.

Prognostic significance of B-cell differentiation genes encoding proteins in diffuse large B-cell lymphoma and follicular lymphoma grade 3

AIM

To define prognostic significance of B-cell differentiation genes encoding proteins and BCL2 and BCL6 gene abnormalities in diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern.

METHODS

In 53 patients with diffuse large B-cell lymphoma and 20 patients with follicular lymphoma grade 3 with >75% follicular growth pattern the following was performed: 1) determination of protein expression of BCL6, CD10, MUM1/IRF4, CD138, and BCL2 by immunohistochemistry; 2) subclassification into germinal center B-cell-like (GCB) and activated B-cell-like (ABC) groups according to the results of protein expression; 3) detection of t(14;18)(q32;q21)/IgH-BCL2 and BCL6 abnormalities by fluorescent in situ hybridization in diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern as well as in GCB and ABC groups; and 4) assessment of the influence of the analyzed characteristics and clinical prognostic factors on overall survival.

RESULTS

Only BCL6 expression was more frequently found in follicular lymphoma grade 3 with >75% follicular growth pattern than in diffuse large B-cell lymphoma (P=0.030). There were no differences in BCL2 and BCL6 gene abnormalities between diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern. Diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern patients were equally distributed in GCB and ABC groups. t(14;18)(q32;q21) was more frequently recorded in GCB group, and t(14;18)(q32;q21) with BCL2 additional signals or only BCL2 and IgH additional signals in ABC group (P=0.004). The GCB and ABC groups showed no difference in BCL6 gene abnormalities. There was no overall survival difference between the diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern patients, however, GCB group had longer overall survival than ABC group (P=0.047). Multivariate analysis showed that BCL6, CD10, and BCL2 expression, BCL2 and BCL6 abnormalities, and International Prognostic Index were not significantly related to overall survival.

CONCLUSION

Diffuse large B-cell lymphoma and follicular lymphoma grade 3 with >75% follicular growth pattern patients have very similar characteristics and their prognosis is more influenced by protein expression of B-cell differentiation stage genes than by tumor cells growth pattern, BCL2 and BCL6 abnormalities, and International Prognostic Index.

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.

Tissue microarray is inappropriate for analysis of BCL6 expression in diffuse large B-cell lymphoma

OBJECTIVE

In this study, our aim was to investigate how different immunohistochemical techniques may influence the result of BCL6 positivity and categorization in germinal center (GC) and non-GC derived diffuse large B-cell lymphoma (DLBCL), as it has been proposed that classification of DLBCL according to cell-of-origin by immunohistochemistry may be performed as a routine procedure in the diagnostic work-up. However, a number of technical issues need to be solved before introducing this as a standard technique.

METHODS

Tumor specimens from 122 patients with de novo stage II-IV disease, adequately treated with anthracycline-containing chemotherapy regimens were collected. Immunohistochemical expression of BCL6, CD10, and MUM-1/IRF4 was examined using a tissue microarray (TMA) technique. BCL6 and CD10 were also evaluated on whole tissue sections.

RESULTS

Due to profound tissue heterogeneity, BCL6 showed a wide range of positivity, with a high number of false negative results by TMA (25% positive), compared to 53% on whole tissue sections (WTS). CD10 was more homogeneously expressed, and TMA results corresponded better to WTS. Consequently, the results from categorization into GC and non-GC DLBCL differed considerably by use of the two methods, and resulted in very different outcome in terms of overall survival.

CONCLUSION

Immunohistochemical GC-status determined on TMA is not reliable enough to be used for individual treatment decisions in DLBCL, mostly due to difficulties in interpreting BCL6 status.

Automated analysis of fluorescence in situ hybridization on fixed, paraffin-embedded whole tissue sections in B-cell lymphoma

Certain recurrent cytogenetic abnormalities are diagnostic of a specific neoplasm and may portend prognosis. As conventional cytogenetics may not reveal a neoplastic clone, and unfixed material for fluorescence in situ hybridization may be unavailable, performing fluorescence in situ hybridization on fixed tissues is diagnostically and prognostically valuable. Manual interpretation of fluorescence in situ hybridization signals may be difficult on paraffin-embedded tissue sections due to truncated nuclei. Therefore, we investigated the use of an automated image acquisition and analysis system (MetaSystems) for interpretation of fluorescence in situ hybridization signals in tissue sections from dual fusion translocation probes. Three probe sets were analyzed on archival specimens with a confirmed diagnosis of mantle cell lymphoma, follicular lymphoma or Burkitt lymphoma. 100% of mantle cell lymphomas (7/7) were positive for t(11;14), 91% of follicular lymphomas (10/11) for t(14;18) and 100% of Burkitt lymphomas (9/9) for t(8;14). Successful hybridization was achieved using various tissue fixatives and fluorescence in situ hybridization interpretation was blinded with respect to the underlying diagnosis. Based on these results, automated analysis of fluorescence in situ hybridization on fixed tissues is accurate and valuable in the evaluation of B-cell lymphoma, and may provide pertinent diagnostic and prognostic information.

A New Method to Make Nuclei or Cell Microarrays

We invented a new method to make microarrays using nuclei extracted from paraffin-embedded tissues or cultured cells. A blank recipient paraffin block with 10 x 10 cores was constructed and sectioned to make the mold for the cell arrays. The sections of paraffin were mounted on poly-L-lysine-coated slides. Prepared nuclei or cells were injected into the cores of the paraffin mold. The slides were dried and dewaxed and nuclei or cell arrays were made. Using this method, we successfully made microarrays of nuclei extracted from diffuse large B-cell lymphoma paraffin-embedded tissues, nasopharyngeal cancer and lymphoma cell lines. This technique resulted in a paraffin-embedded cell preparation that yielded a cell density of approximately 500 to 1000 or 800 cells on average per 0.6-mm-diameter core. The microarrays were successfully used in fluorescence in situ hybridization, mRNA in situ hybridization, and cytohistochemical staining.

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.