Molecular diagnosis in cytology and its place in the new classification : a pactical guide

The clinical importance of molecular testing for Epidermal Growth Factor Receptor (EGFR) mutations and ALK gene rearrangements in non-small cell lung cancer (NSCLC) is widely recognized. As most patients with NSCLC present with advanced stage disease not suitable for surgical resection, only cytology or small biopsy specimens are available for molecular testing in most cases. Although currently targetable genetic alterations are known to mostly occur in adenocarcinomas, accurate histological subtyping of NSCLC can be challenging in cytology and small biopsy samples. The recent IASLC/ATS/ERS International Multidisciplinary Classification of Lung Adenocarcinoma helps provide guidelines for histological subtyping in small samples and tissue management for molecular testing. This review places the use of cytology specimens in the new adenocarcinoma classification and highlights key issues for performing testing in these specimens.