Supplementary Material for: Sustained Remission Following Lung Resection of Isolated Pulmonary Stage III Epithelioid Trophoblastic Tumor: A Case Report

Background: Epithelioid trophoblastic tumor (ETT) is a rare form of gestational trophoblastic disease (GTD) that primarily affects women of reproductive age. The presence of extrauterine ETT poses additional challenges in management, as treatment guidelines remain inconsistent. Fertility preservation is often a key consideration in this patient population. This article highlights a case of ETT with isolated sole site metastasis to the lower lobe of the left lung. It was successfully managed with surgical resection, leading to sustained remission in a premenopausal woman desiring future pregnancies. Case Presentation: A 34-year-old woman (G2P1011) presented with persistent low-level beta-human chorionic gonadotropin (β-HCG) elevation for over three years with no clear underlying cause. She was being followed by her primary gynecologist for a menstrual abnormality, reporting the passage of 'grape-like' clots with menses, but was otherwise asymptomatic. Initial workup spanning 2019 - 2020 including pelvic ultrasound, magnetic resonance imaging (MRI) of brain and pelvis, and positron emission tomography-computed tomography (PET-CT) were negative for radiographic abnormalities. When the β-HCG level notably increased in 2023, the patient was treated at an outside hospital with three doses of methotrexate for presumed ectopic pregnancy. Her β-HCG levels remained elevated despite this treatment. Follow-up skull-base-to-mid-thigh PET-CT revealed a lobulated hypermetabolic nodule in the superior segment of the left lower lobe of the lung. No other disease was identified on PET-CT, pelvic US, or MRI brain. The patient underwent a video-assisted thoracoscopic surgery (VATS) wedge resection, and pathological analysis confirmed ETT. Within two weeks postoperatively, her β-HCG levels declined to <3.0 mIU/mL and have remained undetectable for 18 months. Conclusion: Epithelioid trophoblastic tumors are among the rarest forms of gestational trophoblastic disease. ETT rarely presents outside the uterus and often demonstrates poor response to chemotherapy. This case report highlights a unique presentation of primary pulmonary ETT, successfully managed with surgical resection alone, achieving sustained remission without chemotherapy. In women of reproductive age with persistently elevated β-HCG levels of unclear origin, ETT should remain a consideration. While surgical management may be a viable treatment option for tumors with sole site metastasis, close postoperative monitoring is essential.