[Molecular diagnostics of cytological specimens].

For lung carcinomas with certain molecular genetic alterations of the ALK, BRAF or EGFR gene, there are targeted therapies that are also approved as first-line therapy. Often, only limited sample material from biopsies is available for molecular pathological testing. In some cases, biopsies with standard and immunohistochemical staining have no or too low tumor content to be used for PCR-based examinations or fluorescence in situ hybridization (FISH) analyses. In such cases, cytological preparations such as bronchus brush smears, transbronchial needle aspiration (TBNA), bronchial lavage, puncture smears from lymph node or peripheral metastases, pleural effusion, ascites, and pericardial effusion can be used. Standard stainings such as HE, Pappenheim, and Papanicolaou as well as immunohistological preparations can be used after morphological analysis and confirmatory diagnosis in order to extract DNA from them or to use them for FISH analysis. A cytopathologist marks the tumor cell areas on the slide beforehand. It is only possible to dissect these areas and extract DNA if the proportion of tumor cells is sufficiently high. In order to carry out a FISH analysis with the cytological preparations, the cytopathologist must draw in areas as small as possible with more than 100 tumor cells. Already stained sections are destained before the hybridization reaction. The aim is to achieve comprehensive diagnostics even with limited starting material and to avoid re-biopsies. Between 2016 and July 2019, 1711 next generation sequencing (NGS) and FISH analyses were performed on cytological preparations at the Department of Pathology of the University Hospital of Cologne. The success rate of 85.9% for NGS examinations was slightly higher than the success rate of 82.8% for FISH analyses.