This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urinary tract, Subject name: Pathology
[{'content': 'Metastasis is least common with \nSelect and explain. \nA. Embryonal cell carcinoma, B. Endodermal sinus tumor, C. Taeratocarcinoma, D. Spermatocytic Seminoma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Also known as endodermal sinus tumor, yolk sac tumor is of interest because it is the most common testicular tumor in infants and children up to 3 years of age. In this age group it has a very good prognosis. In adults the pure form of this tumor is rare; instead, yolk sac elements frequently occur in combination with embryonal carcinoma.', 'role': 'assistant'}]