Small biopsy diagnosis of anterior mediastinal masses: histologic, immunohistochemical, and molecular considerations

Anterior mediastinal masses often present a diagnostic challenge, as a variety of lesions can develop in this location. A variety of minimally invasive techniques are currently used to evaluate these lesions, including fine needle aspiration (FNA) biopsy, core needle biopsy (CNB), and endobronchial ultrasound-guided sampling. Thymic epithelial tumors (TET), mediastinal lymphomas, neuroendocrine tumors (NET) and germ cell tumors are the most common lesions found in the anterior mediastinum. They can be difficult to diagnose using minimally invasive techniques as they can exhibit morphological heterogeneity, overlapping histopathologic and cytologic features, and sampling limitations. Review literature and personal experience to evaluate the diagnostic role of minimally invasive biopsy techniques for anterior mediastinal masses, with emphasis on FNA, CNB, and endobronchial ultrasound-based approaches. Practical considerations related to specimen triage and the use of immunohistochemistry (IHC) and molecular assays are discussed. CNB and endobronchial ultrasound (EBUS)-mediastinal cryobiopsy frequently provide sufficient materials when combined with rigorous specimen triage, robust IHC, and molecular assays for the diagnosis of most TET, NET, germ cell tumors and selected lymphomas and often provide higher sensitivity and specificity than FNA. Minimally invasive biopsy techniques play a central role in the evaluation of anterior mediastinal masses. Optimal diagnostic accuracy depends on appropriate biopsy selection, adequate tissue sampling, and the integration of ancillary studies to support accurate classification and clinical decision making. This review briefly summarizes for pathologists, thoracic surgeons and oncologists the histologic, immunohistochemical and molecular considerations of the most frequent anterior mediastinal lesions.