B80-5-01 Diffuse Cystic Lung Disease as an Unusual Presentation of EGFR-Mutated Lung Adenocarcinoma

Abstract Introduction Cystic lung lesions are a relatively common finding on imaging, but determining their underlying cause can be diagnostically challenging. The differential diagnosis for diffuse pulmonary cysts is broad and can range from benign to inflammatory conditions such as pulmonary emphysema, cystic bronchiectasis, interstitial pulmonary fibrosis, and certain infections. Cavitary lesions are uncommon in metastatic lung adenocarcinoma, and the presence of diffuse cystic changes is exceedingly rare.1,2 Recognition of this atypical pattern is critical to avoid misdiagnosis and delay in care. Case Presentation Our patient is a 58-year-old woman with a history of diabetes and hypertension who presented with a month of cough, chest tightness, and exertional dyspnea. She denied smoking or known environmental exposures. Family history was pertinent for lung cancer in her father. Chest CT demonstrated innumerable bilateral thick-walled pulmonary cysts with upper-lobe predominance, associated nodular opacities, and sclerotic vertebral lesions at T11 and L1 (figure 1). Initial infectious workup including streptococcus pneumoniae antigen, legionella antigen, AFB culture, and RPP were all negative Given the diagnostic uncertainty, the patient underwent a video-assisted thoracoscopic (VATS) wedge resection for definitive tissue diagnosis. Histopathologic examination of the right upper lobe and right middle confirmed adenocarcinoma (Figure 2,3). Molecular testing identified an EGFR mutation. Discussion Lung adenocarcinoma, the most common histologic subtype of nonsmall cell lung cancer, exhibits highly variable imaging characteristics and is often identified as a peripheral solid or part-solid nodule with spiculation, pleural indentation, or air bronchogram.3,4 In contrast, diffuse cystic changes are exceptionally uncommon, especially when involving both lungs.5 This case highlights an exceedingly rare manifestation of metastatic lung adenocarcinoma presenting as diffuse cystic lung disease in a never-smoking Asian woman with an EGFR mutation. The diffuse, symmetric cystic transformation of the lungs mimicked benign cystic disorders, complicating diagnosis. The mechanism of parenchymal cyst formation in NSCLC remains uncertain, but proposed explanations include a one-way (check-valve) effect from tumor obstruction of terminal bronchioles and ischemic necrosis from vascular infiltration leading to alveolar dilation.6,7 In our case, the pattern of tumor invasion supported the latter mechanism, suggesting that vascular involvement caused alveolar ischemic dilation and subsequent cyst formation. This case highlights the need to consider malignancy among the causes of diffuse cystic lung disease and the value of early biopsy and molecular testing in identifying a treatable EGFR-mutated adenocarcinoma. This abstract is funded by: None