Diagnostic endoscopic investigations in lung cancer

Distinguishing nonsmall cell lung cancer (NSCLC) from small cell lung cancer (SCLC) is of paramount importance, since the treatment and prognosis of the cancers are often significantly different. SCLC is well known to exhibit massive lymphadenopathy, direct mediastinal invasion and paraneoplastic syndromes [1]. However, there is considerable clinical overlap between NSCLC and SCLC such that clinical differentiation is often not possible and pathological diagnosis is essential. A small number of patients who are unfit for any oncological or surgical treatment and are candidates for best supportive care only may not benefit from pathological diagnosis. In these patients, a clinical diagnosis of lung cancer may have to suffice on the basis of imaging alone. The remaining majority of patients undergo various investigations to determine the histological subtype. An initial diagnosis should be pursued from the most distal site of suspected disease in order to provide staging as well as diagnostic information. Cytology or histology may be provided for pathological analysis, depending on the source and technique employed to generate the sample. Either histology or cytology can discriminate NSCLC from SCLC. Although histology may generally be preferred, cytological samples are also reliable, particularly for NSCLC. Meta-analysis of data from sputum, bronchoscopy and transthoracic needle aspiration compared cytology to histology samples for patients with NSCLC and SCLC [2]. The probability of diagnosing NSCLC in error on the basis of cytology was 0.02 (range 0.01–0.07); however, the converse is less robust. A diagnosis of SCLC had a probability of actually being a NSCLC of 0.09 (range 0–0.33). Therefore, if a diagnosis of SCLC is made on a cytological sample, but the clinical and radiological findings are discordant with the cytological diagnosis, then a histological biopsy should be obtained where possible [2]. In order to achieve a tissue diagnosis of lung cancer, patients may undergo sputum cytology analysis, bronchoscopy, transbronchial needle aspiration (with or without endobronchial ultrasound guidance), endoscopic ultrasound fine needle aspiration, or surgical procedures; these are discussed below. Radiologically guided transthoracic sampling is discussed in chapter 7 in this European Respiratory Monograph.