Lung Adenocarcinoma Presenting as Diffuse Interstitial Lung Disease: A Case Report and Literature Review.

Lung adenocarcinoma (LUAD) is the most common subtype of non-small-cell lung cancer and a leading cause of cancer-related mortality worldwide. Although it typically presents as a solitary pulmonary nodule or mass, it can rarely mimic interstitial lung disease, complicating diagnosis and delaying appropriate treatment. We report a 55-year-old male firefighter who presented with a 3-month history of persistent nonproductive cough, predominantly nocturnal, and recent onset of hoarseness. He denied hemoptysis, weight loss, or fever, and his past medical history included ischemic heart disease, hypertension, and a prior brief episode of cough. He was a heavy smoker. Initial laboratory investigations and bronchoalveolar lavage excluded eosinophilic pneumonia and drug-induced pneumonitis. Chest computed tomography revealed mediastinal lymphadenopathy and multiple left-sided pulmonary nodules. The patient underwent right video-assisted thoracoscopic surgery with wedge resection of the right upper lobe, mediastinal lymph node biopsy, and pleural biopsy. Histopathology confirmed invasive moderately differentiated LUAD, with mediastinal and pleural involvement. Immunohistochemistry showed positivity for CK7, CK20, and TTF-1 and negativity for CDX2. This case underscores the diagnostic challenge of LUAD presenting with atypical radiological features resembling pulmonary fibrosis and highlights the importance of integrating clinical, radiological, and pathological findings, with early tissue sampling critical when conventional therapy fails. Molecular testing and personalized therapy, including targeted agents and immunotherapy, are essential in guiding management and improving outcomes. Clinicians should maintain a high index of suspicion for malignancy in patients with unusual respiratory presentations to ensure timely diagnosis, accurate staging, and optimal therapeutic intervention.