A 36-year-old man presents to his primary care physician complaining of painless enlargement of the testis. Fuher laboratory studies reveal an increase in serum hCG. Of the following, which is the most likely diagnosis?

Seminoma is the most common germ cell tumor of the testis. Serum hCG levels, elaborated by syncytiotrophoblasts, are elevated in about 15% of cases, but these elevations are not as high as those seen in choriocarcinoma. The tumor is highly radiosensitive and often curable, even when metastatic. The peak incidence is in 3rd decade of life Histology : uniform cells with clear cytoplasm and central nucleus, with a prominent nucleolus giving it a fried-egg appearance, with delicate fibrous septa containing a lymphocytic infiltrate. Dysgerminoma represents the ovarian counterpa of seminoma. Embryonal carcinoma is highly pleomorphic and is much less responsive to therapy than seminoma. Yolk sac tumor is the most common tumor of the testis during infancy and early childhood and is usually accompanied by an increase in serum a-fetoprotein.