Seminoma is accurately described by which of the following statements?

Seminomas tend to grow slowly and metastasize late. They usually present as a nonpainful lump that does not transilluminate. They represent about 40% of malignant testicular tumors; embryonal cell carcinoma and teratocarcinoma each represent about 25%. Because most tumors have mixed elements, they are usually classified according to the most malignant cell type encountered, whatever the predominant cell type. When metastases occur, they are usually along the regional lymphatic drainage pathways to the iliac, aortic, and renal lymph nodes. Because of their slow growth and radio-sensitivity, seminomas are associated with a 90% 5-year survival rate. Therapy generally consists of removing the affected testis and sampling the lymph nodes (usually external iliac) for evidence of metastasis. If metastases are present, radiation therapy is given locally to areas of known involvement. Radiation therapy is highly effective in seminoma, and metastatic disease may be palliated for extended periods.