Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration: Diagnostic Criteria, Classifications, Pitfalls and New Cytological Techniques

Lung cancer is the most common cancer in the world with a multifactorial etiology. Age and lung exposure to carcinogens such as tobacco smoke or pollutants have typically been considered risk factors. In recent years, the proportion of non- smokers among lung cancer patients are also on the rise. Carcinoma is the most common malignancy of the lung, with the predominant histological types being adenocarcinoma, squamous cell carcinoma, small cell lung cancer and large cell carcinoma.

The importance of cytology is emphasized as personalized medicine enables longer life expectancy. Delays in diagnosis impose a significant economic and social burden on healthcare organizations and society emphasizing the importance of standardized and uniform approaches when diagnosing lung malignities.

In this dissertation, we focused on samples obtained by endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) for lung cancer diagnosis. We investigated the diagnostic criteria, classifications, and pitfalls of EBUS-TBNA and how the multiplex technique can help in the diagnosing process of these cytological specimens when the cellularity of the specimens is low.

We found that the lack of standardized classification systems for pulmonary cytology adds to the complexity of diagnostic practices, as consistent terminology and criteria impact uniformity. A standardized terminology system is essential to improve consistency and reproducibility at institutional, national, and international levels.

Routine diagnostics and classification terminology require a multidisciplinary approach both inter- and intra-laboratories to ensure diagnostic reliability. Insufficient samples and ectopic tissue are a considerable challenge, often disrupting accurate diagnostics. We performed a root cause analysis of insufficient samples which highlighted that the criteria for sample adequacy are not well-defined. Quality assurance rounds revealed inconsistencies in diagnoses and Papanicolaou classifications both among and within laboratories, illustrating the problematic nature of existing practices.

Multiplex immunohistochemistry/immunofluorescence (mIHC/IF) offers a promising solution, especially for the diagnosis of limited samples, as it allows the simultaneous use of multiple biomarkers, improving diagnostic depth and reliability. The use of mIHC/IF add medical value by providing comprehensive insights into tissue architecture, intercellular interactions, and disease heterogeneity.

Laboratories must address the issues in routine diagnostics and classification terminology to avoid diagnostic failures, emphasizing the need for a multidisciplinary approach to ensure uniform practices across settings.