Pathology & Diagnostics

Burkitt's Lymphoma -- The Message from Microarrays

Harris, NL & Horning, SJ, 2006. N. Eng. J. Med. 354(23):2495-2498

Intro. Paragraph

Two articles in this issue of the Journal, by Dave et al. and Hummel et al., report on the use of gene-expression microarray technology to improve the accuracy of the diagnosis of Burkitt's lymphoma. The two studies differ in many important ways, but both reach the same conclusion: the gene-expression profiling of cases classified as Burkitt's lymphoma by expert pathologists identifies a characteristic genetic signature that clearly distinguishes this tumor from cases of diffuse large-B-cell lymphoma. Furthermore, the microarray method seems to outperform the expert pathologists: 17 percent and 34 percent of cases with the gene-expression signature of Burkitt's lymphoma had been called diffuse large-B-cell lymphoma or unclassifiable high-grade B-cell lymphoma; 0.4 percent and 4 percent of cases without the Burkitt's signature had been called classic or atypical Burkitt's lymphoma; and 3 percent and 8 percent of cases diagnosed as diffuse large-B-cell lymphoma or unclassifiable high-grade B-cell lymphoma had a Burkitt's signature. . . .

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Molecular Diagnosis of Burkitt's Lymphoma

Dave, SS et al., 2006. N. Eng. J. Med. 354(23):2431-2442

Abstract

Background The distinction between Burkitt's lymphoma and diffuse large-B-cell lymphoma is crucial because these two types of lymphoma require different treatments. We examined whether gene-expression profiling could reliably distinguish Burkitt's lymphoma from diffuse large-B-cell lymphoma. Methods Tumor-biopsy specimens from 303 patients with aggressive lymphomas were profiled for gene expression and were also classified according to morphology, immunohistochemistry, and detection of the t(8;14) c-myc translocation. Results A classifier based on gene expression correctly identified all 25 pathologically verified cases of classic Burkitt's lymphoma. Burkitt's lymphoma was readily distinguished from diffuse large-B-cell lymphoma by the high level of expression of c-myc target genes, the expression of a subgroup of germinal-center B-cell genes, and the low level of expression of major-histocompatibility-complex class I genes and nuclear factor-{kappa}B target genes. Eight specimens with a pathological diagnosis of diffuse large-B-cell lymphoma had the typical gene-expression profile of Burkitt's lymphoma, suggesting they represent cases of Burkitt's lymphoma that are difficult to diagnose by current methods. Among 28 of the patients with a molecular diagnosis of Burkitt's lymphoma, the overall survival was superior among those who had received intensive chemotherapy regimens instead of lower-dose regimens. Conclusions Gene-expression profiling is an accurate, quantitative method for distinguishing Burkitt's lymphoma from diffuse large-B-cell lymphoma.

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A biologic definition of Burkitt's lymphoma from transcriptional and genomic profiling

Hummel, M et al., 2006. N. Eng. J. Med. 354(23):2419-2430

Abstract

Background The distinction between Burkitt's lymphoma and diffuse large-B-cell lymphoma is unclear. We used transcriptional and genomic profiling to define Burkitt's lymphoma more precisely and to distinguish subgroups in other types of mature aggressive B-cell lymphomas. Methods We performed gene-expression profiling using Affymetrix U133A GeneChips with RNA from 220 mature aggressive B-cell lymphomas, including a core group of 8 Burkitt's lymphomas that met all World Health Organization (WHO) criteria. A molecular signature for Burkitt's lymphoma was generated, and chromosomal abnormalities were detected with interphase fluorescence in situ hybridization and array-based comparative genomic hybridization. Results We used the molecular signature for Burkitt's lymphoma to identify 44 cases: 11 had the morphologic features of diffuse large-B-cell lymphomas, 4 were unclassifiable mature aggressive B-cell lymphomas, and 29 had a classic or atypical Burkitt's morphologic appearance. Also, five did not have a detectable IG-myc Burkitt's translocation, whereas the others contained an IG-myc fusion, mostly in simple karyotypes. Of the 176 lymphomas without the molecular signature for Burkitt's lymphoma, 155 were diffuse large-B-cell lymphomas. Of these 155 cases, 21 percent had a chromosomal breakpoint at the myc locus associated with complex chromosomal changes and an unfavorable clinical course. Conclusions Our molecular definition of Burkitt's lymphoma clarifies and extends the spectrum of the WHO criteria for Burkitt's lymphoma. In mature aggressive B-cell lymphomas without a gene signature for Burkitt's lymphoma, chromosomal breakpoints at the myc locus were associated with an adverse clinical outcome.

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Personalized medicine and development of targeted therapies: The upcoming challenge for diagnostic molecular pathology. A review.

Dietel M & Sers C, 2006. Virchows Arch. 448(6):744-55.

 Abstract

Due to continuous technical developments and new insights into the high complexity of many diseases, molecular pathology is a rapidly growing field gaining center stage in the clinical management of tumors as well as in the pharmaceutical development of new anti-cancer drugs. The application of novel compounds in clinical trials has revealed promising results; however, the current diagnostic procedures available for determining which patients will primarily benefit from rational tumor therapy are insufficient. To read a patient's tissue as "deeply" as possible, in the future, gaining information on the morphology and on genetic, proteomic, and epigenetic alterations will be the upcoming task of surgical pathologists experienced in molecular diagnostics to provide the clinicians with information relevant for an individualized medicine. Among the different high-throughput technologies, DNA microarrays are now the first array approach close to enter routine diagnostics. Technically advanced and well-established microarray platforms can nowadays be evaluated by distinct bioinformatic tools capable of identifying both novel genes associated with disease development and clusters of genes predicting clinical outcome of an individual tumor. The automatic, highly parallel analysis of proteins and complex proteins lysates for early detection of cancers such as breast, prostate and ovary as proteomic patterns in the serum also appears at the horizon. In addition, an improved analysis of tumor samples via antibody or reverse-phase protein arrays is likely to provide the pathologist in the future with information about activated oncogenic signaling pathways and other cell functions, such as drug response or the potential to metastasize. While expression microarrays and proteomic analysis rely on relatively unstable material incompatible with paraffin-embedded tissue samples, an investigation of DNA methylation using specialized high-throughput platforms has revealed the potential of being used in future diagnostics. Each of these approaches on its own might not suffice to extract all information required for an efficient individualized diagnostics. Therefore, a "multiplex approach" combining the different biological levels DNA, RNA, and protein, may be necessary to functionally classify malignant tumors. This appears to become a major challenge for diagnostic pathologists.

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Written for the card-carrying histo- and immunopathologist, this article clearly describes the goal of microarray, proteomic and epigenetic analyses of expression and the state-of-the-art status of these approaches for diagnosing and staging tumors.

Demystified...tissue microarray technology.

Packeisen J et al., 2003.  Mol. Pathol. 56(4):198-204.

 Abstract

Several "high throughput methods" have been introduced into research and routine laboratories during the past decade. Providing a new approach to the analysis of genomic alterations and RNA or protein expression patterns, these new techniques generate a plethora of new data in a relatively short time, and promise to deliver clues to the diagnosis and treatment of human cancer. Along with these revolutionary developments, new tools for the interpretation of these large sets of data became necessary and are now widely available. Tissue microarray (TMA) technology is one of these new tools. It is based on the idea of applying miniaturisation and a high throughput approach to the analysis of intact tissues. The potential and the scientific value of TMAs in modern research have been demonstrated in a logarithmically increasing number of studies. The spectrum for additional applications is widening rapidly, and comprises quality control in histotechnology, longterm tissue banking, and the continuing education of pathologists. This review covers the basic technical aspects of TMA production and discusses the current and potential future applications of TMA technology.

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Comment

Written more as a technique-lite paper for pathologists considering becoming molecular, this won’t be your first choice as a med student assignment. This article considers tissue sampling, cataloging and other technical issues related to obtaining reliable samples from conventional pathological samples. It could be very useful for enticing educators in histology and pathology courses to discuss genetics/genomics.