Tissue microarray technology: principles, pitfalls and perspectives—lessons learned from hematological malignancies
Introduction
Rapid translation of molecular discoveries, such as therapeutic drug targets or specific, diagnostically-useful, molecular changes, to potential clinical applications has become an important issue in modern medical science. The majority of diagnostic and drug targets are comprised of specific receptors, enzymes or ion channels, all being proteins localized either on/within the diseased cell or within the surrounding cells. Therefore, sub-cellular compartmentalization and cellular distribution (‘micro-topography’), as well as prevalence and clinical significance of specific protein expression on large specimen collectives are of particular importance. Moreover, genome alterations, such as specific chromosomal translocations, gains and losses, and gene amplifications, which are easily detected by in situ hybridization methods, can be associated with prognosis and distinct drug responsiveness (e.g. HER2 gene amplification in breast cancer). Analysis of the expression and clinical significance of such potential targets and signatures at the cellular level also provides important information for modern diagnostics and therapeutics. Tissue microarray technology (TMA) allows rapid and simultaneous morphological assessment of such molecular targets in large collectives of tissue specimens under standardized conditions (Kononen et al., 1998; rev. by Simon and Sauter, 2002).
Section snippets
General principles
For TMA construction, cylindrical cores are acquired from morphologically-representative areas of paraffin-embedded tissue samples (donor blocks) and arrayed tightly into a recipient paraffin block (Fig. 1) using a precision instrument (www.beecherinstruments.com; www.chemicon.com). When tissue cores have a diameter of 0.6 mm, up to 1000 samples can be assembled within a single recipient block of conventional size. Thus, (1) simultaneous analysis of a large number of cases (2) under standardized
Possible pitfalls
Although major concerns have been expressed regarding dismissing heterogeneity on TMA, the TMA approach is designed for high throughput population-based phenotypic and genotypic examinations and not in-depth individual case analysis. It is inevitable that some alterations in minor tissue components will not be detected in individual cases, but the likelihood of hitting such a microheterogenous part will be equal in all cases. Thus, increasing the number of cases and cores analyzed will allow
Evaluation of TMA
TMA sections are suitable for all in situ analyses, including immunohistochemistry and in situ hybridization, as are conventional large sections (Kononen et al., 1998; Schraml et al., 1999; Tzankov et al., 2003b). Still, there are at least two important differences in the use of TMA compared to conventional large section studies. (1) TMA analyses allow an exceptional level of laboratory procedure standardization, thereby reducing intra- and inter-laboratory variations. Importantly, even if
TMA types
Normal tissue arrays are of particular interest in the determination of the organo- and histotypic distribution and expression pattern of candidate diagnostic and therapeutic targets (e.g. search for antigens by new antibodies).
Multitumor TMA are important if the specific qualitative and quantitative target distribution within different neoplastic diseases is screened. Importantly, since the introduction of TMA analyses, many antigens considered to be tissue- or neoplasm-specific have been
Hodgkin lymphoma
Whether a prototypic heterogeneous neoplasm such as Hodgkin lymphoma (HL), with only a few tumor cells dispersed in a background of reactive cells (Fig. 1, Fig. 5), can be successfully analyzed on TMA has been controversial. However, we and others (Garcia et al., 2003; Garcia-Cosio et al., 2004; Tzankov et al., 2003b, Tzankov et al., 2003c; Tzankov et al., 2005) convincingly demonstrated the reliability of this method in HL, though the proportion of non-informative cores on TMA was about 20%.
Perspectives
The major goal of medical scientific research is clinical application for the benefit of our patients. High throughput molecular screenings have generated data that exceed the rate at which biological significance and clinical relevance can be determined. Therefore, despite the dramatic increase in molecular knowledge about pathogenesis and disease progression with detection of many potential diagnostic and therapeutic targets, only a few discoveries have been translated into practical
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