A 28-year-old woman presents to her gynecologist with complaints of intermittent vaginal bleeding, persistent fatigue, and mild pelvic pain. She also mentions recent shortness of breath and a mild cough over the past two weeks. She denies fever, abdominal swelling, or recent pregnancies. On physical examination, she appears pale but stable. Speculum examination reveals dark blood in the vaginal canal with no visible lesions. Her uterus is mildly tender on bimanual examination and appears slightly enlarged. The gynecologist orders a serum beta-hCG test, which returns markedly elevated at 125,000 IU/L. An ultrasound of the pelvis reveals a heterogeneous, highly vascular mass in the uterine cavity. A chest X-ray reveals multiple nodular lesions in both lungs. Biopsy reveals dimorphic neoplasm characterized by mononucleate cytotrophoblast and intermediate trophoblast, intimately admixed with multinucleate syncytiotrophoblast. The lesion shows prominent hemorrhage due to its extensive pseudovascular network. It also has central necrosis. What is the most common precursor to this neoplasm?
