C78-15 When the Clot Wasn’t: Pulmonary Artery Intimal Sarcoma Revealed by EUS-FNA

Introduction Primary pulmonary artery sarcoma (PPAS) is an exceptionally rare and aggressive malignancy, with an estimated incidence of 0.001-0.03% and fewer than 500 cases reported since its first description in 1923. It often mimics pulmonary thromboembolism due to overlapping clinical and radiographic features, leading to frequent misdiagnosis and delayed treatment. Among the histological subtypes, intimal sarcoma—originating from vascular endothelium—is the most common. Due to its deep location and nonspecific symptoms such as dyspnea and chest pain, antemortem diagnosis is challenging and often achieved only through surgical resection or autopsy. Here, we report a rare case of PPAS successfully diagnosed antemortem using endoscopic ultrasound-guided fine needle aspiration (EUS-FNA). Case Description A 72-year-old man presented with a six-month history of exertional dyspnea and chest discomfort. Initial evaluation at a local hospital suggested pulmonary embolism based on contrast-enhanced CT. Upon referral to our hospital, PET/CT revealed strong FDG uptake in the left pulmonary artery (SUVmax 18.4), suggesting a malignant lesion. Given the unusual findings and difficulty in obtaining tissue from the intravascular lesion, EUS-FNA was performed. Histopathological analysis of the aspirate revealed atypical spindle-shaped cells, positive for vimentin and weakly positive for α-SMA, confirming a diagnosis of intimal sarcoma. The patient received palliative radiation therapy (17 Gy/2 fractions) to the right pulmonary artery to alleviate symptoms, followed by doxorubicin-based chemotherapy. Despite treatment, his condition deteriorated, and he passed away 25 weeks after admission under best supportive care. Discussion This case illustrates the importance of considering PPAS in the differential diagnosis of atypical pulmonary embolism, especially in patients who do not respond to anticoagulation and when imaging reveals contrast enhancement within the suspected “embolus” on contrast-enhanced CT—an abnormal finding for thromboembolism, suggesting a malignancy. Due to the tumor’s rapidly progressive nature, timely recognition is crucial. Although the diagnosis is often delayed because of nonspecific symptoms—such as cough, hemoptysis, dyspnea, and chest pain—approximately 50% of patients already have pulmonary metastases, and around 16% have distant metastases at the time of diagnosis. While imaging modalities like CT and PET/CT are helpful, definitive diagnosis requires tissue sampling. Although prognosis remains poor without surgical resection—median survival being 9.0 months without surgery (versus 36.0 months with complete surgical resection)—the use of EUS-FNA may facilitate earlier diagnosis and treatment planning. Our case contributes to the limited literature on diagnostic strategies for PPAS and demonstrates a novel application of EUS-FNA in thoracic oncology.