Two case reports of gastric signet ring cell carcinoma with pulmonary metastasis manifesting as diffuse ground-glass opacities and pleural involvement: an atypical imaging pattern mimicking lung infection.

BACKGROUND: Gastric signet ring cell carcinoma (SRCC) typically metastasizes to the liver and peritoneum. Although pulmonary metastasis occurs in approximately 15% of patients with advanced gastric cancer and typically presents as multiple well-circumscribed nodules on chest computed tomography (CT), diffuse ground-glass opacities (GGOs) as the predominant manifestation of SRCC lung metastasis are exceedingly rare. This pattern may pose a diagnostic pitfall by closely mimicking infectious or interstitial lung diseases.

CASE DESCRIPTION: We report two cases of gastric SRCC with pulmonary metastasis presenting primarily with respiratory symptoms and atypical imaging features. Case 1: A 64-year-old woman presented with persistent cough, dyspnea, and chest pain, and denied any preceding gastrointestinal symptoms. Chest CT revealed bilateral diffuse GGOs accompanied by pleural effusion and thickening. Despite empirical antibiotic therapy directed against Streptococcus pyogenes and Klebsiella pneumoniae identified by next-generation sequencing, her symptoms worsened. Positron emission tomography-computed tomography (PET-CT) demonstrated intense metabolic activity [maximum standardized uptake value (SUVmax) 6.2] in the lung lesions and bilateral pleural involvement. Bronchoscopy-guided biopsy confirmed adenocarcinoma with signet ring cell features, and gastroscopy with biopsy of a depressed gastric angle lesion confirmed poorly differentiated gastric adenocarcinoma. She received docetaxel plus oxaliplatin chemotherapy with symptomatic improvement and was discharged. Case 2: A 62-year-old woman presented with exertional dyspnea and intermittent cough, also without preceding gastrointestinal symptoms. CT imaging demonstrated right pleural effusion, pleural thickening, and ground-glass nodules. Empirical antibiotic therapy was ineffective. Pleural fluid analysis revealed elevated carcinoembryonic antigen (CEA; 85.00 µg/mL) and cancer antigen 125 (CA125; 327.00 U/mL). Biopsy of an adnexal mass and gastric lesions confirmed gastric SRCC with pleural and ovarian metastases. She was referred to the oncology department for systemic therapy. Long-term follow-up data for both patients are not available in the medical records.

CONCLUSIONS: These cases highlight an atypical imaging pattern of gastric SRCC metastasis-diffuse GGOs with pleural involvement-that closely mimics benign lung diseases. In patients without known malignancy who present with unexplained respiratory symptoms, diffuse pulmonary infiltrates, pleural effusion or thickening, and poor response to anti-infective therapy, early lung or pleural biopsy is essential to prevent diagnostic delay and initiate timely systemic oncological treatment.