C63-06 Two Cases of Pulmonary Arterial Intimal Sarcoma Associated With Lynch Syndrome: An Extraordinarily Rare and Treatable Entity

Abstract Introduction Pulmonary arterial intimal sarcoma (PAIS) is extraordinarily rare in the context of Lynch syndrome; only two prior cases of Lynch-associated PAIS are documented in the literature. We describe two additional cases and their surgical and oncological management. Case 1 A 52-year-old woman with known Lynch syndrome (due to familial MLH1 mutation) complicated by colonic adenocarcinoma status-post sigmoidectomy presented with pleuritic chest pain. Computed tomography (CT) demonstrated a large left main pulmonary arterial (PA) occlusion consistent with pulmonary embolism (PE) Image. Despite continuous anticoagulation, she experienced progressive dyspnea and palpitations; repeat imaging consistently re-demonstrated vascular occlusion without interval improvement. Referral for chronic thromboembolic disease (CTED) evaluation prompted concern for intravascular malignancy; positron emission tomography (PET) imaging demonstrated high uptake in the left main PA. She was referred for pulmonary endarterectomy, upon which a large left pulmonary intra-arterial mass with extension to the main PA and pulmonic valve was visualized. The mass was successfully excised in its entirety, with requisite pulmonic valvular replacement. Biopsy pathology demonstrated intimal sarcoma; genetic testing was positive for MLH1 germline mutation and microsatellite instability-high (MSI-H) phenotype. She received adjuvant pembrolizumab for two years; to date, she remains without evidence of recurrence. Case 2 A 42-year-old woman with known Lynch syndrome (due to familial MSH2 mutation) was evaluated for a six-month history of persistent cough with interval development of left-sided chest pain. CT revealed a large left main PA occlusion with extension into the left upper and lower lobar branches, suggestive of high-burden pulmonary embolism. Despite four months of anticoagulation, she experienced increasing dyspnea and chest pain. Repeat imaging demonstrated no vascular improvement, prompting CTED referral and PET imaging, which demonstrated high uptake in the left main PA. She was referred for pulmonary endarterectomy, during which a large myxoid mass involving the left main PA and pulmonic valve was excised; the valve was salvaged. Biopsy pathology demonstrated initial sarcoma (MSH2 positive with MSI-H phenotype) with positive margins; residual endovascular soft tissue was visualized on post-operative CT. She was committed to adjuvant pembrolizumab; following two years of treatment, all endovascular disease has resolved. Discussion Although not classically considered as part of the Lynch tumor spectrum, Lynch syndrome-associated sarcomas are being documented with increasing frequency. Lynch-associated PAIS remains extremely rare, but should be considered in any Lynch patient with new or persistent pulmonary vascular occlusion. Both patients responded well to a combination of pulmonary endarterectomy and adjuvant immunotherapy. This abstract is funded by: None