prognosis for each stage. Spermatocytic seminomas, a tumor frequently found in dogs, is a rare variety occurring in elderly men. It almost never spreads.
    Seminoma is discovered generally in the fourth decade of life and has on occasion been confused with histiocytic lymphoma (the testis is the most frequent site of lymphomas that do not start in lymph nodes).

Non-seminoma  Men with non-seminomatous testis tumors have an average age 10 years younger than that for seminoma, the mid-thirties. These tumors are composed of various cell types as seen under the microscope—embryonal carcinoma , teratoma, yolk-sac or endodermal sinus carcinoma and choriocarcinoma .
    More than 90 percent of non-seminomatous germ cell tumors have more than one cell type in them—embryonal cell carcinoma with or without seminoma, embryonal cell carcinoma with or without yolk-sac tumor and with or without teratoma, and so on. Pure embryonal carcinoma, pure teratoma and pure yolk-sac tumor each account for 2 to 3 percent and pure choriocarcinoma for 0.03 percent.
    Embryonal cell carcinoma, a primitive cell type having the capacity to change into all the cell varieties listed above, is an aggressive tumor. But it is less aggressive than the choriocarcinoma variety, which is full of blood vessels and, therefore, spreads quickly by the bloodstream. Rapidly multiplying tumors like seminoma, embryonal cell and, to a lesser extent, teratocarcinoma are more solid masses that can outgrow their blood supply, producing cystic or "dead tissue" areas inside the tumor.