A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 10-year-old boy is brought to his pediatrician after discovering a painless mass in the left testicle. Results from tumor markers and a biopsy are as follows:
AFP 350 ng/mL (normal value < 10 ng/mL)
hCG 0.4 IU/L (normal value < 0.5 IU/L)
Biopsy: Presence of glomeruli-like structures with a central capillary within a mesodermal core, lined by flattened layers of germ cells.
What is the most likely diagnosis in this patient?
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A
Classic seminomaIncorrect. Classic seminoma occurs in young adults, not 10-year-olds, and does NOT produce AFP (its elevation rules out seminoma).
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B
ChoriocarcinomaIncorrect. Choriocarcinoma produces hCG from syncytiotrophoblasts; this patient's hCG is normal.
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C
TeratomaIncorrect. Teratoma has variable histology with multiple germ layer elements; it does not show pathognomonic Schiller-Duval bodies.
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D
Yolk sac tumorCorrect. Schiller-Duval bodies (glomerulus-like structures) plus markedly elevated AFP in a young boy define yolk sac tumor.
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E
Embryonal carcinomaIncorrect. Embryonal carcinoma occurs in young adults, often elevates both AFP and hCG, and shows pleomorphic primitive cells without the Schiller-Duval bodies that are pathognomonic for yolk sac tumor.
↑ Tap an answer to reveal the reasoning
Answer: D. A child with a painless testicular mass, markedly elevated AFP, normal beta-hCG, and Schiller-Duval bodies on biopsy (the 'glomerulus-like' structures of central capillary surrounded by germ cells) has a yolk sac tumor (endodermal sinus tumor). This is the most common pediatric testicular germ cell tumor, typically diagnosed in boys younger than 4 years.
Schiller-Duval bodies are pathognomonic: a central blood vessel surrounded by a layer of flattened cuboidal tumor cells, resembling a glomerulus. AFP is elevated because yolk sac tumors recapitulate the fetal yolk sac — the source of AFP production in utero. AFP levels >1000 ng/mL strongly suggest yolk sac tumor.
Classic seminoma occurs in young adults (not children), shows a uniform sheet of cells with clear cytoplasm and fried-egg appearance, and does NOT produce AFP (AFP elevation rules it out). Choriocarcinoma produces hCG (which is normal here) from syncytiotrophoblastic cells. Teratoma can have variable markers but the classic Schiller-Duval body is yolk sac. Treatment of pediatric yolk sac tumor is orchiectomy plus platinum-based chemotherapy; prognosis is generally good with appropriate therapy.
**Why each option:**
**A.** Classic seminoma occurs in young adults, not 10-year-olds, and does NOT produce AFP (its elevation rules out seminoma).
**B.** Choriocarcinoma produces hCG from syncytiotrophoblasts; this patient's hCG is normal.
**C.** Teratoma has variable histology with multiple germ layer elements; it does not show pathognomonic Schiller-Duval bodies.
**D.** Correct. Schiller-Duval bodies (glomerulus-like structures) plus markedly elevated AFP in a young boy define yolk sac tumor.