Pulmonary lymphangitic carcinomatosis (PLC) is the diffuse infltration of lymphatic systems by adenocarcinomas. Because of its vague clinical symptoms and absence of malignant features, confrmatory diagnosis requires transbronchial or open-lung biopsy. Tumor spread is postulated to occur by means of retrograde lymphatic permeation with tumor growth along the lymphatic channels and involvement of vascular endothelial growth factor-C in a signaling pathway. The authors describe the case of a 45-year-old woman whose presentation with cough and dyspnea led to diagnosis of pulmonary lymphangitic carcinomatosis with superimposed pulmonary hypertension, tumor thrombotic microangiopathy, and ultimately metastatic signet ring cell gastric adenocarcinoma. Because of the patient's poor prognosis, she was given palliative care and died 29 days after admission. This case emphasizes the importance of the osteopathic principle of treating the whole patient and evaluating all organ systems. Physicians should be aware of PLC from gastric adenocarcinoma and consider it in patients with pulmonary symptoms who are unresponsive to antibiotics.