Pulmonary lymphangitic carcinomatosis and pathological fracture as the initial manifestations of occult gastric adenocarcinoma mimicking interstitial lung disease: a case report and review of the literature

Background Pulmonary lymphangitic carcinomatosis (PLC) clinically and radiologically mimics interstitial lung disease (ILD), posing diagnostic challenges when the primary malignancy is occult. Case presentation A 33-year-old male presented with progressive cough, dyspnea, and a rib fracture following minimal trauma. Chest CT showed bilateral interlobular septal thickening and mediastinal lymphadenopathy. Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) of subcarinal nodes confirmed metastatic adenocarcinoma, with immunohistochemistry (CK7+,TTF-1−, Napsin A−) suggesting gastrointestinal origin. Subsequent PET-CT and gastroscopy identified a 4.0 cm gastric angulus tumor, biopsied as moderately to poorly differentiated adenocarcinoma with signet-ring cells. Despite first-line and second-line chemotherapy with transient improvement, rapid progression ensued. The patient died on February 18, 2025, with an overall survival of approximately 6 months from metastatic diagnosis. Conclusion This case illustrates that in young patients with ILD-like imaging and low-energy fractures, PLC warrants consideration even without gastrointestinal symptoms. Early use of EBUS-TBNA and PET-CT may facilitate timely diagnosis in appropriate clinical settings. Signet-ring cell-associated PLC carries a dismal prognosis, and transient responses should not be misconstrued as long-term benefit.