B80-5-34 Lung Cavitations: The Hidden Face of Invasive Mucinous Adenocarcinoma

Abstract Introduction Invasive mucinous adenocarcinoma (IMA) is a rare subtype of lung adenocarcinoma (∼5%) with a worse prognosis and frequent diagnostic delay, as clinical and radiographic features often mimic infection or inflammation. Delays are especially likely when patients fall outside the traditional lung-cancer risk profiles. Case Presentation A 74-year-old woman with no tobacco exposure history and seropositive rheumatoid arthritis (RA) on immunosuppression presented with several months of fatigue, productive cough, and 50-lb weight loss. Prior to admission to the hospital, she had a four-month long outpatient non-invasive sputum and serological work-up for diffuse multifocal cavitary lung disease that was non-diagnostic. On admission, CT chest showed progression with bilateral multifocal cavitary consolidations. Given recent travel to India and exposure to a family member with possible tuberculosis, an extensive infectious and autoimmune evaluation was pursued. Bronchoscopy with bronchoalveolar lavage grew Pseudomonas aeruginosa with negative studies for atypical bacteria, fungi, and mycobacteria. One month later, robotic-assisted bronchoscopy with transbronchial biopsies confirmed invasive mucinous adenocarcinoma. Staging demonstrated thoracic nodal involvement consistent with regionally metastatic disease. Because of poor performance status, disease extent, and underlying RA, she was not a candidate for cytotoxic chemotherapy nor immune checkpoint inhibition. Discussion IMA typically manifests as multifocal, multilobar, bilateral consolidations that resemble pneumonia or organizing inflammation; cavitation can occur but is uncommon. In our case, malignancy was lower on the differential due to the presence of multiple factors including cavitary lesions, patients’ non-smoking status, and coexisting RA, all of which complicated the clinical picture. While RA is well known for its pulmonary manifestations, including interstitial lung disease and nodules, its association with an increased risk of lung cancer is much less recognized. In parallel, lung cancer in non-smokers—an increasingly recognized growing subset—often presents atypically and may not prompt early oncologic evaluation. Our case highlights the need to broaden our diagnostic lens beyond traditional risk factors in order to: 1) maintain a high index of suspicion for malignancy in patients with RA who present with atypical or non-resolving pulmonary findings, 2) recognize the diagnostic challenge of lung cancer in non-smokers, whose presentations often deviate from classic lung cancer paradigms, and 3) keep IMA in the differential diagnosis of cavitary pulmonary lesions, especially when infectious and autoimmune evaluations are unrevealing. This abstract is funded by: None