C80-49 When Cavitary Disease Isn’t Infectious: A Multidisciplinary Diagnostic Journey to Uncover Pulmonary Mucinous Adenocarcinoma

Abstract Introduction Pulmonary cavitary disease is characterized by the presence of gas-filled spaces within areas of pulmonary consolidation, mass, or nodule. While infectious etiologies—such as Mycobacterium tuberculosis and fungal infections—are the most common causes, a range of noninfectious conditions must also be considered. These include primary lung malignancies, sarcoidosis, and vasculitis. Among pulmonary malignancies, mucinous adenocarcinoma represents a rare histologic variant, accounting for approximately 1% of lung cancer cases. Accurate diagnosis requires a thorough clinical history, multidisciplinary evaluation, and targeted diagnostic workup to ensure timely identification and optimize patient outcomes. Case Presentation A 38-year-old male presented with a four-month history of intermittent cough and progressive shortness of breath. Examination revealed left-sided chest lag, decreased tactile fremitus, and diminished breath sounds over the left mid-basal region. Laboratory evaluation showed WBC 14.5 × 109/L with a left shift; comprehensive respiratory workup was negative. Chest CT revealed inhomogeneous mediastinal densities (largest 3.6 × 2.7 × 2.9 cm) and an irregular lesion in the posterior segment of the left lower lobe (5.4 × 5.9 × 5.3 cm). He was initially treated empirically for atypical pneumonia with azithromycin and then doxycycline for 10 days each, without improvement.Initial bronchoscopy was nondiagnostic. Repeat bronchoscopy with molecular profiling showed tumor cells positive for CK7 but negative for TTF-1, Napsin A, and PD-L1, consistent with mucinous adenocarcinoma. Video-assisted thoracoscopic surgery with pleural biopsies confirmed metastatic mucinous carcinoma of pulmonary origin (CK7 and TTF-1 positive; CK20, CDX-2, and CD117 negative). He was referred to oncology and started on chemoimmunotherapy, achieving a favorable radiologic response and maintaining good functional status (ECOG 0-1) on follow-up. Conclusion This case highlights the diagnostic challenges of cavitary pulmonary disease, particularly when initial clinical and radiologic findings suggest infection. Despite empirical treatment for atypical pneumonia, the patient’s persistent symptoms and negative infectious workup necessitated a multidisciplinary, holistic approach, including repeat bronchoscopy, molecular profiling, and surgical biopsy. This comprehensive evaluation ultimately led to the diagnosis of pulmonary mucinous adenocarcinoma. Early recognition through collaborative, interdisciplinary care allowed timely initiation of chemoimmunotherapy, resulting in favorable radiologic and functional outcomes. This case underscores the importance of considering malignancy in nonresolving cavitary lesions and demonstrates how coordinated, multidisciplinary evaluation can optimize patient care. References: 1) Gadkowski, L Beth, and Jason E Stout. “Cavitary pulmonary disease.” Clinical microbiology reviews vol. 21,2 (2008): 305-33, table of contents. doi:10.1128/CMR.00060-07 2) Gafoor, Khalid et al. “Cavitary Lung Diseases: A Clinical-Radiologic Algorithmic Approach.” Chest vol. 153,6 (2018): 1443-1465. doi:10.1016/j.chest.2018.02.026 This abstract is funded by: None