[Current diagnosis in pathology].

The introduction of modern methods into research and daily diagnostic practice of pathology has brought about major advances. In the middle of our century electron microscopy gave new insights into the ultrastructure by increasing the resolution one thousand times as compared to classical light microscopy. Immunofluorescence and histochemistry allowed assessment of functional and morphologic changes. Important new information was gained by the introduction of immunohistochemistry. The ability of antibodies to bind to epitopes even in formalin-fixed and paraffin-embedded tissues allows the precise diagnosis in many poorly differentiated tumors. The combination of different techniques (as for example immunohistochemistry and electron microscopy in the case of immuno-electronmicroscopy) lead to important new findings. The application of molecular biologic methods was a major step forward. They allow to precisely detect genomic sequences. Complementary strands are synthesized (so called probes), labelled and allowed to hybridize to the nucleic acid sequence looked for. Several examples are shown. The detection of viral nucleic acids (many of which can not reliably be identified on routine histological sections) can be achieved by in situ hybridization. The demonstration of bacteria which are slowly growing (as mycobacteria) or cannot be successfully cultivated can be easily achieved after amplification of specific nucleic acid sequences by the polymerase chain reaction. Molecular biological techniques are indispensable in cancer research (as shown here by the demonstration of IGF2 in nephroblastomas) but are also important in the diagnosis of tumors (as shown by the presence of T-cell-receptor-rearrangement in the case of suspected T-cell-lymphoma).(ABSTRACT TRUNCATED AT 250 WORDS)