C78-21 A “Hairy” Case of Leukemia Diagnosed via Endobronchial Ultrasound (EBUS) Cryobiopsy

Abstract Introduction Endobronchial ultrasound (EBUS)-guided sampling has been the preferred initial tool for evaluating hilar and mediastinal lymphadenopathy. However, the diagnostic yield of EBUS-transbronchial needle aspiration (EBUS-TBNA) is limited and not recommended as a first-line diagnostic tool in patients with high suspicion for a lymphoproliferative disorder, especially indolent subtypes, due to its small sample volume and inadequate tissue architecture for comprehensive evaluation. Emerging evidence supports EBUS-guided cryobiopsy (cryoEBUS) as a superior alternative, offering larger, better-preserved specimens. We present a rare case of hairy cell leukemia (HCL) presenting with mediastinal and hilar lymphadenopathy that was diagnosed using EBUS-guided cryobiopsy. Case Report A 37-year-old woman with hypertension, type 2 diabetes, and prior tobacco use presented with a one-year history of progressive fatigue and mild left upper quadrant discomfort. Notably, she had persistent leukopenia (WBC: 2.6–3.0 K/uL) with relative lymphocytosis (∼52%) but denied systemic “B” symptoms. Imaging revealed moderate splenomegaly and mild retroperitoneal lymphadenopathy. A CT scan of the chest confirmed borderline enlarged mediastinal and hilar lymph nodes (up to 1.2 cm). PET-CT demonstrated moderate FDG uptake in the spleen and mildly active lymph nodes (SUV 2.3–3.2).Given persistent lymphadenopathy and nonspecific clinical findings, EBUS-guided cryobiopsy was performed. Histopathology revealed atypical lymphoid cells with characteristic cytoplasmic projections. Immunohistochemistry confirmed a kappa light chain-restricted B-cell population and a BRAF V600E mutation, establishing the diagnosis of HCL. The patient remains clinically stable and continues to follow with hematology. Discussion HCL is a rare indolent B-cell leukemia marked by pancytopenia and splenomegaly. Lymphadenopathy is uncommon at presentation, particularly involving thoracic lymph nodes. Diagnosis typically relies on peripheral blood smear and bone marrow biopsy. This case illustrates an unusual initial presentation with mediastinal involvement and highlights the diagnostic utility of cryoEBUS when traditional biopsy sites and methods are impractical or non-diagnostic.CryoEBUS enables the retrieval of high-quality tissue suitable for immunophenotyping and molecular testing, overcoming the limitations of TBNA in diagnosing lymphomas and rare hematologic malignancies. Literature reports a diagnostic yield of 87% for lymphoma via cryoEBUS, compared to just 12% with TBNA. To our knowledge, this represents the first published case of HCL diagnosed through cryoEBUS, underscoring its expanding role in diagnosing hematologic diseases. Conclusion This case highlights the expanding role of cryoEBUS in hematologic malignancies, especially in atypical presentations where conventional biopsy sites are inaccessible, offering a safe, minimally invasive approach that facilitates timely and accurate diagnosis. This abstract is funded by: None