[Fluorescence in situ hybridization. A new diagnostic dimension in cytology]

Fluorescence in situ hybridization (FISH) is a powerful method for the identification of chromosomal aberrations to improve the diagnostic performance of cytology. FISH is applicable to almost any type of cytological specimen irrespective of cell type, staining or fixation modality. Multi-target tests for the simultaneous analysis of four chromosomes or chromosomal loci improves the sensitivity of cytological diagnosis in bladder and lung cancer and is most helpful in equivocal cytology. FISH also allows a reliable distinction between malignant mesothelioma and reactive mesothelial cells. Specific translocations can easily be detected by FISH for precise diagnosis of lymphomas and sarcomas. Testing for HER-2 amplification has become a standard method to select patients with breast cancer for therapy with trastuzumab. Co-analysis of HPV and selected genes could become a useful approach in gynecological cytology. The spectrum of diagnostic FISH applications is continuously growing.