A80-3-21 More Than Just a Pulled Muscle: A Rare Presentation of Primary Mediastinal Germ Cell Tumor

Abstract Introduction A slowly growing painless swelling on the chest may seem benign in young healthy males, but it can mask a malignant and aggressive tumor, leading to delayed diagnosis. We present a very rare and atypical presentation of primary mediastinal germ cell tumor (GCT) that infiltrated through the sternum and presented as an external chest wall mass. Case Presentation A 37-year-old male patient with no significant medical history presented for evaluation of a lesion over his sternum. Initially, he thought he strained a muscle. It was tender at first, but later the pain resolved. Despite the lesion, he remained physically active, and his daily activities were unaffected. Over the course of five months, the lesion gradually increased in size, prompting further evaluation. Physical examination showed a palpable, non-tender mass over the sternum. Magnetic resonance imaging of the chest showed a large 15x9 centimeters anterior mediastinal mass infiltrating the sternum. Computerized tomography (CT) confirmed sternal invasion with a pathological fracture through the inferior sternal body, and a mass effect on the heart, without cardiac invasion. Transthoracic echocardiogram was unremarkable. Serum alpha-fetoprotein (AFP) and β-human chorionic gonadotropin levels were elevated. Tissue biopsy revealed GCT. Testicular ultrasound and further imaging did not reveal evidence of primary gonadal GCT or metastatic disease, confirming the diagnosis of primary mediastinal non-seminomatous GCT. He received four cycles of VIP (etoposide, ifosfamide, and cisplatin) chemotherapy with excellent initial response. At three-month follow up, the mass was no longer palpable, and chest CT showed significant decrease in tumor size. However, eight months later, AFP levels were elevated again, and he received high-dose chemotherapy along with sternal resection. He is currently under close surveillance, with no signs of relapse. Discussion GCTs typically arise in the gonads and affect young males. Extragonadal GCTs, like primary mediastinal GCTs, are less common and often present with shortness of breath, chest pain, or cough. It is exceedingly rare for these tumors to invade through the sternum and present as a chest wall mass. Evaluation should include detailed history and physical examination, chest imaging, laboratory tumor markers, and if necessary, a biopsy. This case highlights a very rare presentation of primary mediastinal GCTs, emphasizing the need for clinical awareness and early suspicion to avoid delays in diagnosis and treatment. This abstract is funded by: None