A 22-year-old primigravida at 12 weeks gestation presents with severe hyperemesis, painless dark vaginal bleeding with passage of grape-like vesicles, palpitations, heat intolerance, and tremor. Examination reveals uterine size 18 weeks, blood pressure 158/102 mm Hg with 2+ proteinuria, and bilateral 6 cm adnexal cysts. Serum βhCG is 620,000 mIU/mL (normal peak ~100,000 mIU/mL), free T4 32 pmol/L with suppressed TSH. Transvaginal ultrasound shows an enlarged uterus filled with a heterogeneous echogenic mass containing numerous small anechoic cystic spaces with no gestational sac, fetal pole, or cardiac activity. The structure marked **A** in the diagram demonstrates this classic "snow-storm" appearance. Which of the following immunohistochemical findings would be expected in this lesion?