A80-4-19 Not All SVC Syndromes Are Lung Cancer: A Rare Mediastinal Germ Cell Tumor

Abstract Introduction Germ cell tumors (GCT) typically originate in the gonads; however, about 2-5% develop in midline locations, with the mediastinum representing the most frequent extragonadal site, particularly in adults between 25 and 35 years of age. Among these GCT, seminomas represent an uncommon but distinct subset. Due to their location, they can produce compressive symptoms including superior vena cava obstruction, airway compromise, and vascular thrombosis. We present an unusual case of SVC syndrome secondary to a mediastinal seminoma in a previously healthy young male. Case Description A 29 year old man with no significant past medical history presented with two weeks of progressive swelling of the face and neck, accompanied by dilated veins on the anterior chest wall. He also noted intermittent right arm pain exacerbated by elevation, facial plethora, anterior chest wall cyanosis, voice changes, and a chronic dry cough with night sweats that had been present for several years but had not recently worsened. On examination, there was facial and upper extremity edema with distended superficial chest veins suggestive of SVC obstruction. A CT of the neck and chest demonstrated a large anterior mediastinal soft tissue mass measuring 8.0 × 7.0 × 6.2 cm, causing compression and occlusion of the superior vena cava, with associated thrombosis extending superiorly into the right internal jugular vein. The patient was started on a heparin infusion and subsequently underwent an image guided biopsy. Histopathology revealed malignant germ cells positive for AE1/AE3, Oct4, and CD117, and negative for P40-CK5/6, Pax8, glypican-3, GATA3, AFP, EMA, CEA, CD30, and hCG, consistent with mediastinal seminoma. He was transitioned to apixaban and initiated on combination chemotherapy with Bleomycin, Etoposide, and Cisplatin. The patient showed clinical improvement in facial swelling and venous distention after initiation of treatment. Discussion Mediastinal seminomas are uncommon extragonadal GCT that usually affect males in their third or fourth decade of life. Chest pain, or dyspnea, the development of SVC syndrome as the initial manifestation is particularly rare. Delayed diagnosis may lead to cerebral edema, airway compromise, and cardiovascular instability. Seminomas typically express Oct4 and CD117 and are negative for AFP and hCG, findings that were consistent with our patients profile. Management includes systemic chemotherapy, which has a high cure rate. This case highlights the importance of considering primary mediastinal germ cell tumors in the differential diagnosis of SVC syndrome, particularly in young male patients without prior malignancy. This abstract is funded by: None