Small-cell lung cancer mistaken for pulmonary embolism

What happened, in summary

This 68-year-old woman had hypertension and diabetes and developed 5 months of cough, sputum production, and shortness of breath with exertion. At an outside hospital in January 2024, CT pulmonary angiography showed filling defects in bilateral pulmonary arteries, especially in branches of the left lingular and lower lobes, and she was diagnosed with pulmonary thromboembolism. Rivaroxaban was started. After 3 months of anticoagulation, her symptoms persisted, prompting evaluation at another institution in April 2024. Repeat CT pulmonary angiography still showed persistent filling defects in the left lower-lobe pulmonary artery and along the lingular segmental artery. Because the defect did not improve as expected with anticoagulation, malignancy became a concern. Blood tests showed elevated CEA at 29.84 ng/mL and neuron-specific enolase at 26 ng/mL. PET-CT revealed a hypermetabolic lesion in the lingular segment of the left upper lobe and anterior basal segment of the left lower lobe, with pulmonary artery invasion. Bronchoscopy showed external compression and narrowing at the superior lingular branch and left lower-lobe bronchus. Endobronchial ultrasound found a solid hypoechoic lesion, and biopsy confirmed small-cell neuroendocrine carcinoma. Immunohistochemistry was positive for TTF-1, chromogranin A, synaptophysin, and NSE, with Ki-67 about 70%. The final diagnosis was small-cell lung cancer with pulmonary artery tumor embolism, a presentation that can mimic ordinary pulmonary embolism. Chemoradiotherapy was recommended, but she declined treatment. No systemic cancer therapy was started, and no further follow-up was available. This distinction mattered because anticoagulation alone could not treat tumor invading the pulmonary artery and delayed diagnosis.